Peter Kay is living proof that you can never be too rich or too famous to write a fan letter. He wrote one to Ronnie Barker once — Barker wrote back in the character of Norman Fletcher on Her Majesty’s Prison notepaper and Kay ended up in front of 2,000 mourners in Westminster Abbey last week giving a eulogy for his comedy hero.

Now another enthusiastic letter from Kay praising the talents of the Dr Who script writer Russell T. Davies has won Britain’s favourite stand-up comedian a guest spot in the new series as the “cold and powerful” villain Victor Kennedy.

This will be a change from Kay’s usual persona as the friendly, homely bloke from Bolton, the town where he was born and still lives with his wife Susan and their two-year-old son, Charlie. Despite being one of TV’s top earners, Kay swears he will never leave the northern industrial town he put on the map with his popular comedy series Phoenix Nights, set in a failing nightclub. Kay played the stingy, embittered wheelchair-bound manager, Brian Potter, as well as several of the other parts, capturing the lowbrow, downbeat air of northern clubland but doing it with affection.

In a spin-off from the cult comedy, Kay and his old schoolfriend Paddy McGuinness went on to develop the characters of the Phoenix’s hopeless doormen in Max and Paddy’s Road to Nowhere.

Kay’s rise to best-loved comic status has been rapid: only six years ago he was telling jokes to taxi drivers on Saturday nights. Before that he’d been, among other things, a mobile disc jokey, a cinema usher, a toilet roll packer and a barman at Bolton’s Mecca bingo hall. His comic talent emerged early when, in a school production of The Wizard of Oz, he came on stage dressed as Lion and cocked his leg on a tree.

Since his first television show, The Services — a mockumentary prefiguring The Office — his ratings have climbed steadily: his DVDs have earned him millions along with his advertisements for John Smith’s bitter (Kay doesn’t drink; his father, Mick, died of alcoholism). Nearly seven million people watched his stand-up TV show, Live at the Bolton Albert Halls.

According to his fans, the secret of Kay’s success lies partly in his kindness — he doesn’t do cruel humour — and partly in his small-town, small-time material. “He has the common touch,” says a Channel 4 producer. “He’s like everyone’s funny uncle in a young person’s body.”