Simon Cowell has admitted he fears he has let his Britain's Got Talent co-star David Walliams spiral out of control on the show.

The pair have a long-running jokey partnership as judges on the ITV talent contest.

Cowell said in a promo video for the new series launch that he was regretting letting Walliams become quite such a big star.

He said of his judging panel, which also includes Alesha Dixon and Amanda Holden: "We get on really well - David can be a pain. I feel a little bit like Frankenstein and the monster.

"He's getting bigger and his ego's getting bigger, and he is literally uncontrollable."

Cowell explained his notoriously high standards in letting contestants through to the next round.

He said: "I think I have higher standards than the other three, that's for sure. Sometimes I look at something and I think it's just a pale imitation of what we've seen before.

"Particularly with the dog acts. When you've had an act as good as Ashleigh and Pudsey who were famous all over the world, some of the dog acts I've seen on the show this year... It's not just that the dogs aren't very good, the owners are terrible. They're just really boring.

"There are a lot of people now who think just because they're going to sing opera, we're all going to jump out of our chairs. And we're not, unless you are amazing. The audience at home, they feel the same way."

Asked why BGT, which is heading into its ninth series, is still so popular, he replied: "Certain shows, I feel, are more about a judge's career than the talent. Not mine. Our shows are about the moment a star is born.

"I keep referring back to Susan Boyle because it's the best example I can give. If you remember watching that first audition, you're watching somebody's life change forever, and I think that is intoxicating.

"I love that and I loved it with Ashleigh and Pudsey, and Diversity, Paul Potts. They're magic moments and you're going to see a lot of those this year."

Walliams was not attending today's Britain's Got Talent launch as he is reportedly away on holiday with his family.

Reports early last month alleged that he and his model wife Lara Stone were "on a break".

But neither Walliams nor Stone's representatives have confirmed this.

The couple married in 2010 and had their first child together - a boy called Alfred - in May 2013.

Walliams revealed in an interview that he stopped one BGT audition to phone a friend - actress Sheridan Smith - after a magician said he wanted to cut her in half for his act.

He said: "A gentleman came on stage called John, a magician. He was very entertaining and his dream woman was Sheridan Smith. He really wanted to saw Sheridan in half.

"Having worked with Sheridan on a play, I can understand what he was saying. We are very good pals so I phoned Sheridan and she spoke to John.

"I'm hoping that one day we can bring the two together and make a dream come true, at least for John."

Britain's Got Talent returns on Saturday at 8pm on ITV.