A government minister has quit his post to take part in a world famous motor race.
Defence minister Lord Drayson will take a leave of absence from the government as he prepares for the 24-hour Le Mans race in France.
Lord Drayson, who is also Labour's largest individual donor, will take part in a series of qualifying heats in the US before competing in the day-long race in France.
The American Le Mans series features four different classes of car and the winner from each class is eligible to take part in the final event.
This year marks the first time bio-ethanol 'green' cars have been eligible for the race.
The 47-year-old peer told Gordon Brown it was a "wonderful opportunity to showcase British motor sport technology for environmentally friendly racing."
In his letter to the prime minister, Lord Drayson said: "As you know I have a passion for motor racing and over the past year have competed in the British GT championship racing a unique bio-ethanol fuelled race car, achieving a 'historic first' win for a green-fuelled car and coming second overall in the championship.
"A number of special circumstances have now presented me with a once-in-a-lifetime opportunity to take my racing to the next level.
"I have the opportunity to race next year in the American Le Mans series in the US, a key step towards my eventual dream of success in the Le Mans 24-hours endurance race."
Mr Brown said he was sorry to lose the defence procurement minister and would look forward to his return to government.
The prime minister continued: "I understand your desire to take up the extraordinary opportunity which has now emerged to achieve your great life's ambition.
"You are of course lucky to have that opportunity but you are showing your customary boldness and imagination by pursuing it."
Lord Drayson has been replaced by Baroness Ann Taylor, who unlike her predecessor will be paid for the post.
His departure comes as a coroner in Oxford rules fusilier Gordon Gentle was unlawfully killed in Iraq.
The coroner found Fusilier Gentle died in Iraq because he did not have the proper equipment to protect him from a roadside bomb.
Rose Gentle, the mother of Fusilier Gentle, condemned Lord Drayson's departure as "insensitive".
She said: "Does he have the right equipment for the race? That's all I can say.
"It's really insensitive timing. He should be at his desk, not trotting off to some race. It just shows another breakdown in the chain of command."