LONDON - McLaren stunned Formula One today by announcing that world champion Fernando Alonso will leave Renault to race for them in 2007.

The 24-year-old Spaniard became the sport's youngest champion this year, winning seven grands prix to beat McLaren's Kimi Raikkonen by 21 points, and last April extended his contract with Renault to the end of 2006.

Alonso also helped the Oxfordshire-based team to the 2005 constructors' title ahead of McLaren, who won 10 races through Raikkonen (seven) and Colombian Juan Pablo Montoya.

"To become part of a team with such a desire to succeed and passion for performance is a dream come true for any Formula One driver," Alonso said in a McLaren statement.

"Obviously I will be sad to leave Renault but sometimes possibilities come along which are just too good to miss."

McLaren team principal Ron Dennis said the announcement had been made to enable all the drivers to concentrate on next season.

It came five days after McLaren announced a title sponsorship deal with mobile phone giants Vodafone who switched from Ferrari.

"We always make it clear that we want to be the best and the only way of achieving this objective is by attracting the best people, the best drivers and the best sponsors," Dennis said in the statement.

McLaren last won the drivers' title in 1999 with Finland's Mika Hakkinen. Finn Raikkonen and Montoya will race for McLaren next season with one of the two making way for Alonso in 2007.

The departure of Alonso, whose personal manager is Renault's team principal Flavio Briatore, will raise further questions about Renault's long term commitment to Formula One.

The French carmakers' president and chief executive Carlos Ghosn said at the French Grand Prix in July that Renault would stay in the sport for as long as there were clear benefits.

Briatore has a contract to the end of 2006 and Renault F1 president Patrick Faure has said the team are committed to Formula One until at least the end of 2007.

"I was disappointed to learn of Fernando's decision but by the end of 2006 he will have spent five seasons with Renault," Faure said in a statement.

"Fresh challenges are essential for any sportsman, and he has taken the decision to pursue a new direction in his career. That is part of Formula One, and part of life."

Alonso was contracted to Renault when they were still racing under the Benetton banner in 2001, paying his dues on loan at Minardi and as a test driver before getting one of the two racing positions in 2003.

He won his first grand prix in Hungary that year and finished sixth in the championship. He was fourth the following year before his stellar 2005 season.

Raikkonen is out of contract at the end of 2006 and has long been coveted by Ferrari as an eventual replacement for seven-times world champion Michael Schumacher.

Brazilian Felipe Massa is joining Ferrari in 2006 but only on a one-year deal while 36-year-old Schumacher's contract expires at the end of next season.

"We are in discussions with our current drivers Kimi Raikkonen and Juan Pablo Montoya regarding the 2007 season," Dennis added.

"Both Juan Pablo and Kimi are extremely talented, professional and competitive Formula One drivers and they have and will continue to concentrate on our joint challenge for the championships."

There will also be the question of who replaces Alonso at Renault in 2007.

Australian Mark Webber, managed by Briatore, will be out of contract with Williams by that point while Renault also have promising Finn Heikki Kovalainen waiting in the wings as their 2006 test driver.