The Contender, which also stars Jeff Bridges, Joan Allen and Christian Slater, focuses on a fictional Republican attempt to de-rail the nomination of a female Democrat as vice-president.

In an interview with Premiere magazine, Oldman and his manager Douglas Urbanski said the movie was biased.

Urbanski said the film, which opened in the US on 13 October, was "almost a Goebbels-like piece of propaganda".

He suggested that next month's presidential election was a factor in the changes, which he claims were paid for by DreamWorks and carried out by the film's writer and director Rod Lurie.

Oldman told Premiere that when DreamWorks bought the finished film, Lurie was paid by DreamWorks to edit it so that Republicans in general were portrayed as villains.

The actor and his manager claim the question of who is just and who is not was left ambiguous before the final cut, and that Oldman actually saw his character as "the only true patriot".

In a later interview with Reuters news agency, Urbanski softened his line.

He said: "There's no question in my mind that not only did Rod Lurie adjust his political beliefs in order to advance his career, he also adjusted the movie in tiny ways in order to please his benefactors."

"There's no indication to me whatsoever that Rod ever felt pressured.

"One only has to look at the coverage of the [Democratic National] convention to see that the owners of this company have sympathies with the Democratic party."

He added: "Did those sympathies enter into the editorial process or the decision to buy the movie? Unequivocally, no."

Director Rod Lurie said that Oldman may be suffering from a strain of Stockholm syndrome in which "they begin to sympathise with their captors, and in this case, the captors are the characters that they play".