The name of the film, directed by Kevin Knoblock, refers to the temperature at which the brain begins to die. It does not pretend to offer a balanced political picture, and in fact was financially backed by conservative research organisation Citizens United.

And Celsius 41.11 is already proving as contentious for US newspaper reviewers as Fahrenheit 9/11, coming at such a politically sensitive time with just weeks to go until the US elections.

Many newspapers, while not disagreeing with the facts of the documentary, have not been impressed with it as a piece of entertainment. Philip Kennicott of The Washington Post called it a 'dull' and 'overlong attack ad on John Kerry'.

Jeffrey Bruner of the Des Moines Register said: 'For the US $900,000 reportedly spent on this film, it's a pretty low-quality production that's not going to transfer well to a big screen. But as after-dinner viewing in your living room, it should work fine.'