Catherine Tate's Nan, a ruthlessly truthful creation, is best taken short. Nan's Christmas Carol (BBC1, Friday), longer than usual and later than usual because of Nan's language, cast her as a combatative Scrooge making three ghosts and her deceased husband sorry they were born. Or died. The most eye- catching ghost was David Tennant, who bore a striking resemblance to Russell Brand.

I haven't always been a fan of Catherine Tate's Nan either, admiring the character work but finding the essential joke a little repetitive. But Catherine Tate: Nan's Christmas Carol managed to refresh two overworked franchises simultaneously: Tate's horrible old lady gag and Charles Dickens' snow-dusted morality tale. Nan makes a perfect Scrooge, hideously unseasonal when Uncle Bob Cratchit turned up on a visit from Yorkshire with his queasily cheerful children. She wasn't exactly pleased with the gift they'd given her - a charity donation to the Mobile Library of Sudan. "It's a picture of an Arab man standing next to a donkey with half-a-dozen copies of The Da Vinci Code strapped to its back," she said witheringly on opening the envelope. It's an alternative present, her great-niece explained. "What... alternative to something I wanted?" she snapped back. She demanded ID from the Ghost of Christmas Past and told the Ghost of Christmas Future that his introductory video was rubbish. Offered the chance to change the future after her admonitory vision of a loveless old age and lonely funeral, the first thing she asked was, "Could they bring back Lovejoy... I do love it."

Remember Nan, the terrifyingly two-faced character from The Catherine Tate Show? Warm and cuddly one minute and swearing like a TV chef the next? It always felt like Nan deserved a life beyond the sketch show, and now she gets it, taking the Scrooge role in what we imagine will be the loosest of adaptations of A Christmas Carol. What a bleedin' liberty!

A Christmas Carol has seen many film and TV incarnations over the years. But this is perhaps the most bizarre and clever of all a comic retelling with Catherine Tate's acid-tongued Nan as Scrooge.

The writers have taken some bleedin liberties with the original story (Tiny Tim is a dog and the ghost of Christmas Present wears skinny jeans) but its a laugh-fest from beginning to end.

The three ghosties are played by Ben Miller, Roger Lloyd Pack and an almost unrecognisable David Tennant, who all attempt to convince Nan to swap her miserly ways for some seasonal cheer.

Nan's Christmas message

Writing specially for the Telegraph, Catherine Tate's famously candid (i.e. spectacularly foul-mouthed) Nan character passes on her seasonal good wishes...

Instead of the usual Christmas special, Catherine Tate has turned Nan into Scrooge, visited by ghosts of Christmas past and her deceased husband. It promises to be utterly appalling - in a good way.