Having hired husband-and-wife team Frances Goodrich and Albert Hackett to brush up the dialogue, Capra turned his attention to casting.

Top of his wishlist was James Stewart; an actor who’d spent his last four years in the air force and was reluctant to return to thesping so quickly.

“Jimmy needed a little persuading,” says Capra Jr. “On set he would say he didn’t want to be an actor any more and that he might go help his dad run his hardware store.

But I have seen my father’s notes and there was only one name for George. And when my dad started to tell him the story, Jimmy said,‘I’m your boy.’”

Shot in the middle of a heatwave in summer 1946 on a built-from-scratch Bedford Falls set spanning four acres of the RKO backlot, the film was a costly investment for Capra’s nascent Liberty Films outfit.

Alas, It’s A Wonderful Life had a relatively short one in cinemas, doing respectable but far from spectacular business before vanishing into the ether.

In fact, the film’s subsequent popularity has more to do with a legal oversight – some berk forgot to renew the copyright – that saw it fall into the public domain in the ’70s.

Repeated ad nauseam on US television, it swiftly became a holiday staple.

“People would ask my father if he was unhappy about not owning it,” says the director’s son. “He would say, ‘Not at all.’ He loved to see it shown and played and enjoyed by audiences old and new.”

The film’s lacklustre performance, however, had one unfortunate side-effect: the enforced sale of Liberty Films to Paramount in 1949.

“For the first time, the ‘one man, one film’ apostle became an employed contract director taking orders,” rued Capra in his autobiography The Name Above The Title.

“It was the beginning of my end as a social force in films...”