News of U.S.President Kennedy's assassination caused the BBC to delay Doctor Who's debut by a day.
This misconception is found mainly amongst American fans. Doctor Who was always intended to be screened on a Saturday. The pilot episode was initially pencilled in for 24th August but was pushed back on several occasions, finally being scheduled to appear at 5:15pm on 23rd November. Kennedy was shot just after 6:30pm GMT on the 22nd and pronounced dead a short time later. The news filtered through to the U.K. in time for the main evening news bulletins, i.e. long after a show intended for a family audience would have been screened. The screening of An Unearthly Child the following afternoon was delayed but only by about ten minutes due to an extended news bulletin.

The first episodes were shown live.
Doctor Who was never shown live, as BBC documentation and the highly informative The Handbook series prove. The misconception appears to stem from an interview Carole Ann Ford gave for the 10th Anniversary Radio Times Special in which she is quoted as saying: "I shall never forget that first episode. It was being transmitted live, and just before we were to go on news came through of President Kennedy's assassination."
Because of its highly technical format, e.g. special effects and the like, Doctor Who was always pre-recorded using the BBC's new video recording equipment. "(T)hat first episode" was actually recorded five weeks earlier on 18th October, whilst the episode being recorded on the fateful day was The Survivors, episode 2 of The Mutants.
The only BBC light entertainment show to be affected by events in Texas was That Was The Week That Was, the legendary live Saturday night satirical news review. The news from America forced a total last-minute rewrite of the planned show, including a rather poignant song for resident singer Millicent Martin to perform. Miss Martin has also been quoted as saying much of what Miss Ford is supposed to have said. Obviously, somewhere along the line, some confusion crept in.

The Daleks got their name from an encyclopedia covering DAL - LEK.
This is a popular misconception put about by Dalek creator Terry Nation when pushed for an explanation of the name. In actual fact, there has never been an encyclopedia published covering entries from DAL to LEK.
However, it is possible Mr.Nation was subconsciously inspired by transposed index files. These have the letters they cover on their spines thus:

Series ratings shot up after the first Dalek episode.
Official BBC figures show that 6.9 million viewers tuned in to watch The Dead Planet. Figures for the following episode, The Survivors, actually show a drop of half a million, despite Barbara's blood-curdling scream at seeing the sink plunger being waved about in front of her. It wasn't until episode three, The Escape, that ratings rocketed, two-and-a-half million extra viewers tuning in to see what all the fuss was about after the Daleks had been revealed in all their glory.

The Krotons were the winning design in a Blue Peter competition.
The competition prize was actually to have the winning design featured in "T.V.Comic's" Dr.Who strip. The Krotons were designed by BBC costume designer Bobi Bartlett and based on descriptions in Robert Holmes' script.

Michael Grade cancelled Doctor Who in 1985 but was forced to change his mind after a huge public outcry.
Whilst it's true some productions were cancelled, Doctor Who was not one of them. With the BBC under pressure from the Thatcher regime to curtail its perceived overspending of public money, and a major new soap serial in the pipeline (EastEnders), new BBC1 Controller Michael Grade had to make savings somewhere. By moving Doctor Who from its winter slot to an autumn slot the following year, it was thought the production team could make its contribution towards the BBC cost-cutting exercise simply by taking a break, which would also allow for a number of recommended changes to be made without the usual pressures of production deadlines impinging. Amongst the few shows that were cancelled was the concluding third series of The Tripods and the long-running children's classic Crackerjack!, whilst Black Adder II faced the axe before its writers assured the BBC management there would be no expensive location filming.
The infamous "Cancellation Crisis" was nothing more than Britain's hysterical tabloid press being fed a few misleading facts and transforming them into a sales-boosting story. At least two national tabloids claimed responsibility for getting the show "reinstated" when Turner and Saward's rather lame The Trial of a Time Lord was included in the 1986 schedules.

The original "Tardis" police boxes were made of wood.
Urban police call boxes were actually constructed from pre-formed concrete panels and had cast iron sides. Only the doors were wood. The panels were formed by pouring cement into wooden moulds which, when set, retained the impression of wood-grain. All-wooden call boxes were only found in rural areas where there was less chance of them being run into by motor vehicles.

The Stones of Blood was filmed at Stonehenge.
This particular misconception was featured in the quasi-travel guide Travels Without the Tardis. The story was actually filmed in the Rollright Stones circle in Oxfordshire where, incidentally, Winston Churchill used to take part in certain Druidic ceremonies. Travels Without the Tardis was written by two Americans and presumably aimed at an American readership, most of whom would appear to be under the impression there is only one stone circle in England when there are, in fact, dozens if not hundreds. Presumably, had the writers been aware of their half-British compatriot's secret lifestyle, the Rollright Stones would have been correctly identified.

The Tardis prop was a left-over from Dixon of Dock Green
The unlikely form of the Tardis was inspired by Australian writer Anthony Coburn seeing police boxes all over London. The prop itself was specially built for Doctor Who by Peter Brachaki.

The Gunfighters was the worst ever Doctor Who story.
The concept of "best" and "worst" is largely objective. In terms of ratings, The Gunfighters ranks above several other stories, including the three that followed it on air, An Unearthly Child, the first, penultimate and last stories from series 6, the first four stories of series 18, and every story from The Trial of a Time Lord on. The "worst ever" tag arose from audience appreciation figures dropping below 2 million for the first time in the show's history, and the reaction of several critics who firmly believe Britain can't make Westerns.

Polly's surname was Lopez.
Polly was one of those companions who was never officially given a surname, like Vicki and Ace. BBC documentation of the time suggests her intended surname was to be "Wright". This idea was probably dropped because it had already been used for Barbara, and a replacement was never considered necessary. The "Lopez" came from Jean-Marc Lofficier, who invented the name from Polly's double in The Faceless Ones, Michelle Leuppi, for his revised Programme Guide in 1989.

William Hartnell was the son of a prosperous Devon farming family.
This was a bit of fiction created by Hartnell to cover up the fact he was born in London and never actually knew his father.

Potatoes were anachronistically featured in The Time Warrior.
Nowhere in The Time Warrior are potatoes seen or mentioned. The mistake was actually made in Terrance Dicks' novelisation, which, until the video release in 1989, was the only reference source available to the general public after the original, and only, screening of the story.

Doctor Who was only intended to run for seven/thirteen weeks.
The original intention was to have Doctor Who running all year round. The misconception comes from BBC Chief of Programmes Donald Baverstock's insistance that the initial production run be broken down into segments of 13 episodes each, so the show could be continually re-assessed. This obviously gave rise to various cast members quoting "We thought it wouldn't last more than seven weeks". When it became clear a continual run would be too much for a regular cast of just four to cope with, it was decided to introduce breaks in the production.

The Beatles appeared in Doctor Who
Well, technically they did in The Chase. However, their "appearance" was a brief clip from a promo film of their latest single Ticket to Ride. Although the Beatles weren't averse to making cameo appearances in TV shows - they appeared in The Morecambe and Wise Show and Blackpool Night Out with Mike and Bernie Winters for instance - their busy schedule made it impossible for them to attend filming sessions for both Coronation Street and Doctor Who. One idea was to have them dressed up as old men still performing their old hits. With both John Lennon and George Harrison failing to make it to their sixtieth birthdays, it's probably just as well this proposal never got beyond the ideas stage.

Doctor Who was originally thought up by Sydney Newman for ABC and came with him when he joined the BBC.
With so many similarities between Doctor Who and Newman's Pathfinders serials, it's tempting to think that one was a direct descendent of the other and had Newman not left ABC, Doctor Who could well have been an ITV show. However, there is strong documentary evidence that the seeds of Doctor Who were being sown by the BBC before Newman's arrival in December 1962. As early as March 1962 in fact, when the Beeb's Head of Light Entertainment, Eric Maschwitz (the man who wrote A Nightingale Sang in Berkely Square), asked the Head of Scripts, Donald Wilson, to prepare a report on the possibility of a series of one-off science fiction adaptations. Wilson delegated the task to drama script editors Donald Bull and Alice Frick, who more-or-less concluded that written-for-TV scripts would work better than adaptations of novels and short stories (although Newman-protegée Irene Shubik commissioned several such adaptations for Out of this World). A further report prepared by Frick and colleague John Braybon was delivered in July 1962, and laid down several of the ground rules later adopted for Doctor Who, for example, no "bug-eyed monsters" and no robots that were obviously men in costumes. In March 1963, Newman discussed the possibility of commissioning a drama series to fill the "gap" between Grandstand and Juke Box Jury with Chief of Programmes Donald Baverstock and Assistant Controller (Planning) Joanna Spicer. After deciding upon a science fiction series for all the family, Newman consulted with Wilson, who duly presented him with Frick and Braybon's report. Wilson came up with the idea of using time travel as a basic plot device and decided there should be a group of regular characters. Script Department writer C.E.Webber developed the basic character profiles. Newman altered Wilson's initial idea slightly, which he considered too high-brow and unimaginative, making it more like Pathfinders, added a teenaged character to Webber's proposed team of "Handsome Young Man Hero", "Handsome Well-dressed Heroine Aged About 30" and "Maturer Man, 35-40, with some Character Twist", and changed the "Maturer Man" to "Frail Grumpy Old Man".
In other words, Sydney Newman may well have influenced the format of the new show, but he was by no means the instigator. It's also debatable that Pathfinders would have evolved into Doctor Who had Newman stayed at ABC, as follow-ons from Pathfinders featuring two of the stars had already been commissioned and screened.

The final episode of The Mutants (aka The Daleks) featured a glass Dalek
Another misconception which arose from a novelisation. The famous Glass Dalek was one of several features of David Whitaker's novel Doctor Who - in an exciting adventure with the Daleks which definitely didn't appear on TV. As was the introduction which had Ian first meeting Barbara and Susan on Barnes Common. A glass Dalek did eventually appear in Revelation of the Daleks over twenty years later.

Inside the Spaceship was written as a filler when The Hidden Planet was belatedly dropped.
The first series of Doctor Who featured several stories that were commissioned but never made and several others that were outlined but never commissioned. Malcolm Hulke's The Hidden Planet was one that was commissioned but later dropped. However, it wasn't removed from the production schedule until a fortnight after Inside the Spaceship had been broadcast, and was originally intended to go out after Marco Polo anyway. Inside the Spaceship was written as a filler but only after Chief of Programmes Donald Baverstock had insisted on a first production block of 13 episodes (An Unearthly Child, 100,000 B.C. and The Mutants totalled 11).

The Dæmons erred by claiming the last Witchcraft Act in Britain was repealed in 1951.
Some sources claim that Barry Letts and Robert Sloman made a mistake by having Miss Hawthorne state the last Witchcraft Act was repealed as late as 1951, claiming instead a date of 1736. What was actually repealed in 1736 was an earlier law which made witchcraft punishable by death. This was replaced by a new law passed in 1735 which changed the punishment to imprisonment. This Act was repealed in 1951 and replaced by the Fraudulent Mediums Act which remains in force today.

Drop-outs from Time Lord society are called Shobogans.
In The Invasion of Time, the group of drop-outs, renegades and exilees led by Nesbin were referred to as the "Outsiders". In The Deadly Assassin, Castellan Spandrell refers to "Sheboogans", but not in reference to the Outsiders. "Sheboogan" could be an Anglicisation of the Manx word "Sheh vaghouin", which means "bearskin", and could be taken to refer to people who wore animal skins. In other words, "barbarians".

Mary Tamm appeared topless in The Sweeney.
When the film Sweeney 2 was first screened on TV, a number of Who fans spotted a resemblance between one of the supporting actresses and Mary Tamm. As this particular supporting actress also appeared topless, the myth soon developed that it was indeed Ms.Tamm. However, as any simple checks would reveal, not only did Mary Tamm not appear in Sweeney 2, she has never bared her breasts for the camera. She did appear nude in a couple of films but was only filmed from the back.
Similarly, a still from the horror flick Vampire Circus purporting to show a topless Lalla Ward is in fact of another actress with long blond hair, and a bigger bust. Although Ms.Ward appeared in Vampire Circus, the only things she revealed were vampire fangs! Her one and only topless shot was in the 1974 soft-porn film Sweet Charity, which was later re-released with extra scenes featuring another actress naked. When Club International magazine published stills of these extra scenes claiming they were of Lalla, she successfully sued.

Ridley Scott was originally assigned to design the Daleks.
This rather groundless rumour arose when the Daleks returned to British TV screens in 2005. Obviously desperate for something sensational and new to write about the Doctor's oldest foes, newspaper feature writers dug around a bit, discovered Ridley Scott had been considered to work on Doctor Who in its early days and assumed he must have had something to do with the design of the Daleks. However, whilst it's true the future Alien director was working as a designer for the BBC at the time, he was never involved with any aspect of Doctor Who's production. Peter Brachaki was originally intended to be the show's permanent set designer but stepped down after working on the pilot episode. Barry Newbery and Ray Cusick took over Brachaki's duties, working on alternate stories. Newbery worked on 100,000 B.C. whilst Cusick oversaw the development of The Mutants from scratch, including the now familiar design of the Daleks.

The Doctor had 28 assistants.
No he didn't, he had three. Of the 28 individuals some sources and commentators claim were assistants, only Liz, Jo and Romana can be regarded as such. Liz and Jo were officially employed by UNIT as assistants to the Doctor in his capacity as UNIT's Scientific Advisor, whilst Romana was appointed his assistant by the White Guardian at the start of the quest for the Key to Time.
That twenty-eight includes two robots, K9 and Kamelion, which, being machines, cannot be classed as assistants. Would you call your car or your PC your assistant? It also includes Katarina and Sara on the basis they accompanied the Doctor in several episodes AND travelled in the Tardis. But then so did a surprisingly large number of others, including the Brigadier, Benton, Laurence Scarman, Duggan, Caris and Deedrix, Richard Mace, Hugo Lang and Herbert Wells, none of whom have ever been described as assistants. It would be more accurate to state that the Doctor had 21 regular travelling companions, 1 assistant (Liz, who never set foot inside the Tardis) and 2 assistants who became regular travelling companions.

The Daleks had a problem with stairs.
Oddly enough, nobody ever questioned the Daleks' ability to climb stairs until around 1988. Before then, the Daleks had always managed with ramps, lifts and hover pads. The only time they encountered steps was in The Chase, where they must have had some levitational power like that demonstrated in Remembrance of the Daleks. The so-called famous scene of Tom Baker's Doctor ridiculing the Daleks' inability to manage stairs was featured in Destiny of the Daleks and actually had the Doctor challenging the Daleks to climb a rope. Somehow, this got misinterpreted as a problem with stairs, which writer Ben Aaronovitch decided to resolve in Remembrance of the Daleks. By 2005, this had obviously been forgotten by the armies of misinformed journalists covering the Welsh series.
n.b. Daleks can't swim either, but that didn't stop one emerging from the River Thames in The Dalek Invasion of Earth!

Doctor Who was transmitted in twenty-six seasons.
The twenty-six separate runs of Doctor Who were never referred to as "seasons" by anybody until Jean-Marc Lofficier misused the term in his Programme Guide in 1981. Rather than being corrected in later editions to the more correct "series", it was adopted by the "super-fans" and eventually spread throughout TV as the Yuppie generation gradually took control of the airwaves. The term "season", in British TV at least, was used to describe the entire output of a particular channel over a certain part of the year. "Seasons" generally ran from the New Year to Easter, from Easter to mid-summer, from mid-summer to autumn, and from autumn to Christmas. Individual shows, including Doctor Who, were always referred to as serials or series, and each new run of Doctor Who was announced on air as being "a new series", never "a new season". Technically speaking, Doctor Who was a series of serials.

Doctor Who was especially popular amongst students.
Who says? There's the story about a student protest at one particular seat of learning being dispersed when the Dean announced Doctor Who was just about to start on the telly, but this is most likely apocryphal. I was a student for five years and hardly any of my colleagues were remotely interested. Yes, the campus TV room was full when An Unearthly Child was re-run in 1981, but by the time Castrovalva came round, everybody was watching Riverside instead! This particular myth probably arose after the rise of the "super-fans" in the late-1980s, most of whom appear to have attended university in Manchester in the early-1980s.
n.b. For the benefit of those who don't know, Riverside was one of a series of depressingly trendy "Yoof" programmes screened on BBC2 after the advent of Punk. Manchester is a particularly depressing city in the north-west of England which has delusions of grandeur far beyond its worth.