He said: "It is with great regret that my time on Big Brother will come to an end... I’ve had the time of my life working on Big Brother’s Little Brother, from our broom cupboard days to the all singing all dancing show we make now."

Dermot explained that the strain of working on Big Brother and X Factor at the same time last summer had been too much.

"This summer’s work commitment of BBLB and the X Factor has proven to me that to do both shows is impractical if not impossible. I want to thank Channel 4 and the Big Brother family for all their support."

Head of E4 Angela Jain said: "BBLB has been Dermot’s little baby from the start. We will miss him and all the laughter and professionalism he has brought with him."

Celebrity Hijack will see a bunch of young artists, athletes and musicians enter the house to compete for a £50,000 prize fund.

Dermot shock over Sharon shoe stunt - Nov 2 2007
Dermot O’Leary has revealed he knew Sharon Osbourne was serious about walking out of X Factor’s first live show, because she took her shoes off.

And the 34-year-old presenter dismissed suggestions her outburst was merely "pantomime", saying: "We love that, that’s what we need on the show."

He added: "I had no idea what was happening, it was my first live show and not only did she walk off, she took her shoes off. That’s when I realised. I think when a woman takes her shoes off that means she means business."

Dermot, who took over from Kate Thornton to host the ITV talent show, said he was enjoying watching the acts develop.

"It’s weird because you watch people on the Thursday doing their soundchecks and then on the Friday they get a bit better, so the people you don’t think nail it first time round get better and better all the time."

And he backed the bookies current favourite and Louis Walsh’s contestant Niki Evans.

"I think Niki has probably been the person so far that’s sort of had the stand out performances. I think that’s what most people think," he added.

Dermot replaces Kate on X Factor - April 1 2007
Dermot O’Leary is the new host of the X Factor, it was announced.

The Big Brother’s Little Brother presenter will front the hit show for the next two series, after Kate Thornton and judge Louis Walsh were axed.

The 33-year-old said: "I was very flattered to be offered the job to host such a hugely successful show."

The hunky presenter, reported to have landed a £1 million X Factor contract, said: "I’m really looking forward to working with Simon and the team on the kind of Saturday night entertainment show I grew up watching."

ITV’s Controller of Entertainment Duncan Gray said: "Dermot is a star. He’s warm, clever and funny and he was our number one choice for the job.

"We’re thrilled to have him on ITV and we’re sure he’ll keep the X Factor the nation’s number one entertainment show for many years to come."

The fourth series, which will feature four judges, kicks off on ITV1 in the summer.

Leona Lewis, winner of last year’s series, scored a No 1 with her single A Moment Like This.