Idris Elba finds it hard to switch off.

The 'Dark Tower' star admits it is difficult for him to ''sit still'' and he says he is always working, no matter what time it is or where in the world he is.

He said: ''It's really hard for me to sit still. Tomorrow I might have nothing to do, but I'll go, 'Now is a good day to write a song.'

''We view it as wrong if human beings can't turn their brain off, but when you've got a brain like mine - one thing that's always building and grasping - to ask it to turn off is odd. For me it feels weird. Even on holiday, I would probably get my computer out and write.''

And the 44-year-old actor admits his body and brain thinks he is a lot ''younger'' than he actually is.

He added to the September issue of The Red Bulletin magazine: ''I had a year to train and mentally face up to all sorts of problems that were in the way - injury and whatnot. He perhaps didn't train as hard as the odds were in his favour from the outset. Perhaps he thought I'd be an easier fighter. But I knew that this was one fight where I could get hurt, and I was dedicated to not letting that happen.

''People asked me, 'Was it [kickboxing] a sort of midlife crisis thing?' To some degree, probably. I've got a body and a brain that think that I'm younger than I am; age is just a number. So I felt it would be interesting to challenge my body again. When I really put my mind to it, no one was going to put me down.''

The full interview is available in the September issue of The Red Bulletin.