Kingsley's new role is more Gandolfini than Gandhi

Kingsley will play himself in the sixth season of the award-winning drama, The Sopranos. Other guests in the show, which is likely to be broadcast in Britain on E4 in the autumn, include the singer Frankie Vallie and actors Hal Holbrook and Julianna Margulies. But the plot line that requires an Oscar-winning British knight is a secret.

When Kingsley, 62, appeared alongside Sopranos' stars James Gandolfini, Edie Falco, Lorraine Bracco and Michael Imperioli at a press conference in America to launch the series' final season, a Mafia-style omerta or vow of silence hung over proceedings.

Asked about his role, Ben Kingsley turned to Colin Callender, president of HBO Entertainment which produces the series, and asked: "How much of this question can I answer?"

Mr Callender said: "If you tell him the storyline, you have to shoot him." Instead Kingsley sang the praises of the script and the stars, explaining that he was asked to appear by its creator, David Chase, and agreed because he found the role was "delightful, witty and extremely well-written".

He added: "I've found the cast, who are bonded like a family, extraordinarily welcoming to me as an outsider. And therefore, because of that welcome and because of the specific nature of that programme and its rhythm, I was allowed to participate in the rhythm of the timing.

So it was a real joy." Chase said only: "Ben Kingsley plays Ben Kingsley."

When pressed to say something more about the new series, he added: "The characters are emphasized, I guess. Obviously, it's always Tony and Carmela, Anthony Jr. Paulie has a lot to do. Vito, Ben Kingsley."

The Sopranos' stars Gandolfini as mobster Tony Soprano with Falco as his wife, Carmela, from whom he separated in the last series. Bracco plays Dr Jennifer Melfi, Tony's psychiatrist, while Imperioli plays Tony's nephew, Christopher Moltisanti.

A trailer for the series screened to US critics suggested that Tony and Carmela have a reconciliation, but that the show retains its quota of shocking violence.

The next 12 episodes, which will be broadcast in America from March, are the sixth series and will be followed by a shorter series of eight final episodes, expected to air next year.

The fifth series concluded with Tony Soprano potentially facing prison - or worse. His position scarcely seems to have improved.

Chase said the mood around the mobster now was "kind of disquieted, sort of rattled, not feeling things are going well".

David Chase insists that once these 20 new episodes are broadcast, it will be the end of the show which has won multiple awards, including five Golden Globes. Although even the cast are unaware of the ending, Michael Imperioli predicted it would not be upbeat.

"I have a feeling most of these characters aren't going to wrap up too well. I don't mean dead. Some dead. I mean I don't think there are going to be too many happy endings, just knowing David's sensibility."

Gandolfini said: "It does feel like the end this time."

There have been rumours of a spin-off film, but the creators have played down the idea.