Karl Urban ''wasn't prepared'' for how demanding it would be playing Judge Dredd.

The 'Star Trek' actor takes up the role of the all-powerful judge, juror and executioner in forthcoming film 'Dredd', but he didn't envisage just how tough it would be to portray the character while he is wearing a Helmet.

He said: ''I don't think I was quite prepared for how demanding it was. To take away the eyes - such a vital and valuable tool for an actor - forces you to use your Body Language and voice.

''The Dredd suit could certainly put you in a mood. We were shooting in Cape Town and it gets pretty steamy, working in full lathers and a helmet.''

Karl insists he ''trained like a mother***er'' to become physically fit for the role - previously played by Sylvester Stallone in 1995 movie 'Judge Dredd' - and he was so worried about the suit's flexibility that he put the costume on two weeks prior to filming to make sure he was comfortable in it.

He added to Total Film magazine: ''I actually got into that suit a couple of weeks before we started filming so I could get used to moving around in it. Ours was a very practical suit. Dredd drives a motorbike so he's got full leathers on and protective body armour.

''We wanted the suit to reflect a seriously f***ed-up Dangerous world. These guys get a shot at just riding down the road!''