The Avengers star is vehemently opposed to the controversial gas extraction method amid fears it could damage the environment, and he previously lobbied to have it banned in New York.

Now Ruffalo has turned his attention to the U.K., where a number of new fracking sites are planned, and he has urged Cameron not to back the proposals.

"Mr Cameron, you're making an enormous mistake, and it's a legacy mistake. Because there's no fracking that can be done safely," he declares during a video interview with environmental campaign group Friends of the Earth. "Your people don't want it. You've already told them once before that if they didn't want it, you wouldn't push them to take it, and you're turning back on your word, sir. And what is a politician if he's not credible..."

Plans to create new fracking sites in the U.K. have sparked a series of protests, and fashion designer Vivienne Westwood has been one of the anti-fracking drive's most prominent voices.

She even drove a tank to Cameron's home in Oxfordshire, England in September (15) to protest against the expansion of fracking in Britain.

Other stars to support the anti-fracking movement include Sir Paul McCartney, Yoko Ono, model/actress Lily Cole, funnyman Russell Brand, and screen stars Helena Bonham Carter and Jude Law, who all signed an open letter to the British government demanding an end to shale gas drilling projects in the U.K.