Most celebrities have to cope with the odd overzealous fan letter, but Amitabh Bachchan, India’s most famous Bollywood actor, gets his portrait drawn in blood. “I’ve received some very frightening ones,” he says. “I tell them to make it a miniature because they are losing a lot of blood. But how do you stop them?”

When Bachchan falls ill, millions of Indians do penance. In 1982 he injured himself in a stunt scene and fell into a coma. “Some 80-year-old women said they ate only one meal a day and would sleep on the ground, praying for my recovery,” he says. “One chap who lived 400km from Mumbai ran backwards from his village to the city and then backwards home again, a total of 800km.”

Bachchan is in Britain for the launch of his film Baabul. The hotel behind Buckingham Palace where he is giving a press conference is abuzz with anticipation and half the UK’s Indian press. Bachchan, 65, in black velvet shirt and gold-crested slippers, looks every inch the glamorous statesman.

Certainly there is no British actor alive who shares his fame. He is Tom Cruise, Sean Connery and Clint Eastwood rolled into one. And Chris Tarrant. He has been hosting (though is due to leave) the Indian version of Who Wants to Be a Millionaire?, drawing a breathtaking 250m viewers. In a BBC online poll in 2000 he beat Laurence Olivier to be voted the greatest actor of the millennium; and yet most people in the West have never heard of him.

The Mumbai-based Bollywood industry churns out more than 1,000 films a year. “Big B” has made 150 and — for a western audience almost as surprising — he hasn’t had a single on-screen kiss.

Bachchan sees such films as “the one national integrator”. They’re a magical blend of dance, song and romance, based on traditional stories that every Indian child, regardless of creed, caste or faith, is weaned on.

“Indian cinema is very rooted in the grassroots of the country,” he says. “We have a lot of people living a meagre existence. What better than to be able to walk into a theatre after a hard day’s work, into a fantasised world, and come out happy after three hours? We give them Indian tradition, happiness, romance. It’s for the common man.”

He made his name playing action heroes in the 1970s and appeared in arguably the greatest Bollywood film ever, Sholay, which is based on The Seven Samurai. He later became known for thrillers such as Sharaabi and Coolie. It was on the set of the latter that he almost died.

Indeed, Bachchan’s fame hasn’t come without problems. The son of a celebrated poet, he grew up in a social set that included the Gandhis and the Nehrus. It was his friend Rajiv Gandhi who coaxed him into politics after the assassination of Rajiv’s mother Indira, then prime minister. It was a disastrous two-year flirtation.

“I came into parliament and realised that politics was something I was totally inadequate for and knew nothing about,” he says.

Allegations were made about his family’s involvement in arms dealing — later proved untrue — but it convinced him that he wasn’t cut out for politics. Negative publicity was not something he was equipped to handle: “Politicians are very strong people and they know how to deal with it. I don’t.”

After a 10-year break from acting, he now relishes roles that have a social message. Baabul deals with the subject of a widow’s remarriage. There are some 33m widows in India because remarriage is taboo in Hinduism: “In some sections of Indian society the young widow of the house is not treated kindly,” says Bachchan.

He is an ambassador for the International Indian Film Academy, an annual Oscars-style event to reward excellence in the Indian movie industry. It has become so popular that Dubai, New York and Amsterdam made bids to hold next year’s event. It is significant, perhaps, that it will be held in Yorkshire.

On his recent trip to the UK for the IIFA inauguration he also found time to meet Gordon Brown, who gave him a book about Nelson Mandela. Bachchan gave Brown a book about himself.

“With the large influx of Asians into Britain, it’s almost like being home,” he says. “Almost everything you get in India you can find here — and the food is often better.”

His son Abhishek is also a famous Bollywood actor and is dating the actress and model Aishwarya Rai. Bachchan and his son may be megastars but an average filming day is 9am to 6pm.

Family, on set and off, is everything: “Every day I like to have one meal with the family, that is my wife and son — my daughter is married — and that is almost a diktat to them.”

Living in this twilight world between godlike fame and family normality, does he find it strange that in India millions of people would do penance for him yet 90% of the world doesn’t know who he is? “No,” he shrugs. He looks to an aide: “In India, Brad Pitt and Angelina Jolie wouldn’t be recognised in most places.”