Sir Ian McKellen’s favourite part of filming The Hobbit was being surrounded by kneeling dwarves, according to Peter Jackson.

The film’s director explained how the dwarves were made to look smaller by having Sir Ian stand on a box, and added: “There’s also Ian’s favourite technique, which was the dwarves on their knees.”

Sir Ian, who plays Gandalf in the film, said: “I adore all the dwarves, they know that. There is one special dwarf and he knows who he is, but enough of that.”

The actor, 73, also spoke about the change involved in switching from playing Gandalf in The Lord of the Rings trilogy to playing him again in The Hobbit.

“He comes back as the most boring man or wizard that could have possibly been invented,” he said. “The beard is gone, he seems to have stopped having any fun and, of course, he has got to save Middle Earth so he’s got a mission. He doesn’t even have a pointy hat.”

Meanwhile, Sir Ian revealed in an interview published on Tuesday that he had had prostate cancer for the last six or seven years, but added that the disease was not life-threatening.

“I’ve had prostate cancer for six or seven years,” Sir Ian told the Daily Mirror tabloid. “When you have got it you monitor it and you have to be careful it doesn’t spread. But if it is contained in the prostate it’s no big deal.”

“I am examined regularly and it’s just contained, it’s not spreading. I’ve not had any treatment.”