It's a Wonderful Life was a film about Christmas.
When the Eighth Doctor told the dark-haired version of Sam Jones about the blonde version of her who travelled with him, she thought it was a practical joke like in It's a Wonderful Life. She said her mum cried through it every time it was on television. (PROSE: Unnatural History)
The Eighth Doctor said that Christmas brought communities together, like in It's a Wonderful Life. (PROSE: Not in My Back Yard)
Peri Brown told the Fifth Doctor that she wanted a Christmas on Earth, which had, among other things, It's a Wonderful Life on TV. (PROSE: Far Away in a Manger)
The Tenth Doctor was looking for his copy of the film when he accidentally released the Wire. After recapturing the Wire with the help of Alice Wu on Christmas Day, the Doctor joined Alice and her family as they sat down to watch the film. (PROSE: Loose Wire)
Behind the scenes
The characters in Flip-Flop are named after characters and actors in It's a Wonderful Life.