100,000 BC - S1-E1
Character mistake: When Ian is trying to escape from the TARDIS in episode 1, he says, "He closed the door from over there, I saw him." It was in fact Susan who closed the door.
Character mistake: The Doctor gets Jo to do some mathematics to distract her. At one point she says "49 x 2=88", when it actually equals 98, then she says that "adding 10 equals 108". (In other words, Jo (Katy Manning) fluffed her line, got one figure wrong, then went back to script...).
Character mistake: The Doctor (Patrick Troughton) makes one of the funniest fluffed lines in the entire history of Doctor Who in the final episode. With all sincerity he says "We'll all be dead soon, unless you switch over to the sexual air supply." (The word Troughton was probably looking for was "sectional.").
Remembrance of the Daleks - S25-E1
Character mistake: The gate to I.M. Foreman's scrapyard reads "I.M. Forman."
Character mistake: When the Doctor is saying the decimals of Pi to avoid falling under the control of BOSS. He gets it wrong; he says "3.1416..." When it's actually 3.141592.
Battlefield - S26-E1
Character mistake: The Brigadier asks the pilot if she speaks Czechoslovakian, even though Czech and Slovak are different languages.
Character mistake: When the Brigade Leader shoots the Primord, he noticeably closes his eye. He is supposed to be a high ranking well trained officer.
Answer: TARDISes are generally available for properly authorised use on Gallifrey; they're not usually assigned to a particular Timelord on a long-term basis. The Doctor stole his when he left his homeworld.
Tailkinker ★