Live Aid organiser Geldof set up the company, best known for Channel 4's morning programme The Big Breakfast, in 1992 along with Charlie Parsons and Waheed Alli.

The deal will put Alli - made Lord Alli by Prime Minister Tony Blair last year - on the Carlton board managing director of the company's Carlton Productions arm.

Geldof and Parsons will keep up their ties with Planet 24 and are understood to be working on new ideas.

Geldof proud of company

Chris Evans' media career took off thanks to Planet 24

Neither company would put a figure on the deal, but City estimates range from between £15m to £30m.

Lord Alli said the tie-up with Carlton - which owns the ITV companies Carlton, Central and Westcountry - made for "boundless" opportunities.

Bob Geldof said: "This is one company that has managed to shift the way television looks so that nowadays our screen is awash with Planet 24 wannabe programming."

A company spokesman said it would retain its identity as part of the Carlton group, and would continue to work on a variety of projects for a number of different broadcasters.

Current TV projects include a Channel 4 show for MTV UK presenter Richard Blackwood. "It'll be a great show. It'll be an old-fashioned variety show, but with lots of hip bands on and lots of energy," said the spokesman. A new film show for Johnny Vaughan is also in the pipeline for C4 to compete with the BBC's Film 99.

Formed from Breakfast merger

Planet 24's impact on British television has been considerable, with many pundits crediting the company for inventing "yoof" TV.

The company was formed by Geldof's Planet Pictures and Alli and Parsons' 24 Hour Television to bid for the Channel 4 breakfast slot, beating 31 rivals to win the show.

The Big Breakfast was a hit from its launch in September 1992, propelling Chris Evans from cult local radio DJ to his current status as TV star and owner of national pop station Virgin Radio.

Its loud, brash style threatened to strange the new ITV breakfast outfit GMTV at birth, and over the years has grown to make stars out of many of its hosts.

Geldof himself conducted a series of interviews with world leaders for the show, while his then-wife Paula Yates had cheeky chats with celebrities on the show's bed.

Cutting-edge reputation

The company's other best-known product is The Word, which started a trend for rowdy, live Friday night programming. Guests flashed, swore and fought on air, while viewers were invited to prove they would do anything to get on TV - such as sitting in a bath of maggots or eating their own vomit.

The company quickly developed a reputation for being on the cutting-edge, and gained new commissions, such as Gaytime TV for the BBC.

In recent years the company has worked on more serious programming, including a documentary with Earl Spencer, entitled Diana, My Sister. Former Conservative cabinet minister Ann Widdecombe hosted a set of mock trials for a programme called Nothing But The Truth.

The company has branched out into radio production. Projects include a BBC Radio 5 Live show for former Treasury press aide Charlie Whelan which is due to start in April.

Geldof happy as public face

Bob Geldof co-founded Planet 24 in 1992

Geldof has always been happy to be seen as the public face of the company - even becoming a radio DJ for six months when Planet 24 signed a deal with Capital Radio to work on projects for alternative radio station Xfm, which it had just bought. However he was derided by the NME as "the world's worst DJ" and listening figures fell.

But the real power behind the company is seen to be Lord Alli - who left school at 16 and was made a peer at the age of 34. In recent years Tony Blair, Peter Mandelson and Culture Secretary Chris Smith have all been guests at his mansion in Kent.

He sits on Panel 2000, a group which advises the government on how to present the right image abroad.