The Underworld star has penned an open letter to Cameron on behalf of People for the Ethical Treatment of Animals (PETA), insisting the politician needs to make good on plans to ensure circus acts are animal-free sooner rather than later after a previous deadline for the ban came and went without any action.

In the letter, Sheen writes, "Following Parliament's instruction to the government back in 2012 to take action, the British public were promised that a ban on wild animals in circuses in England and Wales would take effect by January, 2015.

"Although that promise has been broken, now is the right time to do the right thing. I urge you to make the ban a reality...

"Wild animals do not voluntarily ride bicycles, stand on their heads or jump through rings of fire. To force animals to perform these meaningless and often uncomfortable or painful tricks, trainers use whips, muzzles, bullhooks and electric prods. The true spirit of the circus is best illustrated by thrilling performances by human entertainers - like clowns and trapeze artists - not by wild animals whose spirits have been broken and who are forced to perform under duress.

"As someone who comes from a family that has included circus performers myself, I would like to see us become a country where animals are treated with respect, not as objects of ridicule.

"The British public clearly agree and have made their feelings on this issue clear. There is no longer any excuse for delaying the ban."