Brad Pitt has admitted that his brood of six children is far harder to look after than roles in any action film.

The 48-year-old actor raises children Maddox (11), Pax (nine), Zahara (seven), Shiloh (six) and Knox and Vivienne (twins, four) with fiancée Angelina Jolie.

Speaking at the London premiere of his new film, Killing Them Softly, he said: "Does it ache? Sure. The knees have gone, the back is crunchy. Getting the kids ready for school is every bit as painful as anything I had to do in this film."

Pitt and Jolie (37) are planning on marrying, but have yet to set a date. "We are going to do it. We haven't set a date yet, though," he said.

"We are getting a lot of pressure from our kids. We could do it in the UK. It has been such an amazing summer here, with all your events - the Jubilee and the Olympics. I've watched everything."