His scene in The Dark Knight was filmed this summer and involves Batman, played by Christian Bale, The Joker, played by Heath Ledger, and Alfred Pennyworth, played by Michael Caine.

'It's a pretty tense scene,' said Mr Leahy, chairman of the Senate Judiciary Committee. 'It's going to be a very interesting one.'

The long-time Batman fan would reveal little about his role other than that he is called the 'distinguished gentleman' and he does not wear tights.

This is not his first brush with the superhero. The Democrat has done voice-overs on Batman cartoons, written the preface for a Batman book and had small roles in the last two Batman features.

He said he would donate his earnings from the film, scheduled to be released next year, to the Kellogg-Hubbard Children's Library in Montpelier, Vermont, where he received his first library card.

ASSOCIATED PRESS