Simon Pegg convinced Benedict Cumberbatch he was being affected by radiation on the set of 'Star Trek Into Darkness'.

Funnyman Simon played a practical joke on cast member Chris Pine - who plays Captain James T. Kirk in the Hollywood sequel - and it quickly spread, with Benedict worrying it was responsible for him messing up his lines.

Simon explained to The Sun newspaper: ''I don't like seeing people get embarrassed.

''But we were filming in a nuclear facility and one day I said that Chris needed neutron cream - otherwise he'd get sunburn.

''He said, 'What?' And I said, 'Yeah, you'll get a rash from ambient radiation in the air.' From there the trick spread to other cast members.

''Finally, we got Benedict. He had this speech and he kept f***ing it up.

''Afterwards he said, 'Guys, I'm ever so sorry - I've got a real headache. I think the ions were getting to me.' He was so convinced.''

Despite missing a few lines, Cumberbatch - who plays villain John Harrison - said he had plenty of fun making the Jj Abrams movie, particularly filming stunt sequences.

He said: ''Working on the stunt sequences and choreographed fight sequences - it was a joy. I felt like a kid in a candy store. There's one point where I said to myself, 'Are you supposed to have this much fun earning a living?' It's just ridiculous.''