Tom Campbell

Tom Campbell was a special police constable from London in the 20th century.

The Dalek Survival Guide indicated that Tom came from a version of reality "B" relative to the First Doctor's version of reality "A". (PROSE: Dalek Survival Guide)

Biography
Tom accidentally boarded the TARDIS, having mistaken it for a genuine police box after being attacked while attempting to foil an armed robbery at a jeweller's shop. He accompanied Dr. Who, his granddaughter Susan and his niece Louise to London in 2150, which had been devastated in the Dalek invasion of Earth several years earlier. Once there, he assisted in freeing Earth from the Dalek occupation.

He was returned to the scene of the crime earlier than he left, therefore allowing him to apprehend the robbers; he overpowered them quickly and drove them away to the police. (TV: Daleks' Invasion Earth 2150 A.D.)

Behind the scenes

 * Bernard Cribbins would later appear on the television series as the recurring character Wilfred Mott, the maternal grandfather of the Tenth Doctor's companion Donna Noble, and who briefly became a companion in his own right. He is the only actor to have portrayed companions in both the movies and the television series. While filming The End of Time, he remarked to outgoing series star David Tennant, "The last time I was in the TARDIS was in 1966." After a slight pause, Tennant noted that he had not even been born yet, causing Cribbins to feel "very, very old".
 * Tom's foiling of the "smash and grab" marks a peculiar instance of time travel in Doctor Who which is at odds with most accounts in mainstream continuity which establish that generally a time traveller cannot go back and change their own personal history. (TV: Father's Day, The Parting of the Ways, The End of Time, The Time of the Doctor) It is of note that the earlier version of Tom who would have entered TARDIS is completely absent from this new version of the event, his place being taken by the present Tom.