When is a police box not a police box?

50 years ago, apart from blowing a whistle, this was the way to communicate with the police….but then, on the night of the 23rd November 1963, that all changed…this was suddenly a Tardis, a space ship belonging to a 900-year-old Time Lord, the Doctor. TARDIS stood for Time And Relative Dimension in Space.
That simple idea, that a spaceship could be bigger on the inside than on the outside, was one of the two brilliant innovations this program had. The second, which came along three years later and ensured the show would last until today, was the regeneration of the main character....in other words, a Time Lord's ability, when dying, to rebuild his body into a new individual. Brilliant.
Happy Birthday, Doctor...