The Prime Minister, Tony Blair, has written a "personal" letter to President George Bush asking him to support the bid.Since the days of President Dwight Eisenhower the fleet of helicopters that land on the south lawn of the White House and take presidents either to Camp David or Andrews Air Force base have been made by US manufacturer Sikorsky.Sikorsky's main challenger is the joint British-Italian company, AgustaWestland, which is offering a three-engine helicopter that it plans to build in the US. Sikorsky is pitching a newly certified twin-engine S-92 whirlybird. Bell Helicopter and Boeing are also contenders.Sources involved in awarding the contract yesterday told The Wall Street Journal that until recently it would have been impossible for a foreign-designed helicopter to be considered for the Marine One fleet. But the source said that because of Britain's continued support of the US over Iraq such concerns had been dropped.Mr Blair wrote to Mr Bush in January to support AgustaWestland's bid, saying: "I hope you will look favourably on this proven 'off the shelf' product." Downing Street last night refused to release the full text of what it said was "personal correspondence" designed to outline that the AgustaWestland helicopter was a proven product that was used by the British, Italian and Canadian military.AgustaWestland's bid has angered those who feel the contract should go to an American company.

Last week Sikorsky's parent company, United Technologies, lost a $3bn (£1.9bn) contract to supply engines to the Airbus military cargo plane. Though United's bid was some 20 per cent lower than that of the winning European consortium, the Europeans used political ties to offer sweeteners to the deal.. The world's leading central bankers attempted yesterday to calm mounting fears over the slump in the dollar as it hit its lowest level against the euro since the single currency was launched four years ago. He was speaking after a meeting of central bankers from the Group of 10 (G10) rich nations that includes the US, the UK, France, Germany and Japan. "The sense was in the case of the euro it was a recovery from weakness rather than remarkable strength," he said.His comments came as the dollar hit $1.16 against the euro for the first time in more than four years after John Snow, the US Treasury Secretary, said the fall had boosted the nation's exports.

It tumbled more than a cent, weakening as far as $1.1624 from $1.1487 late on Friday, close to the euro's $1.16675 starting rate in January 1999. Sterling also fell against the euro, touching fresh lows of 72.13p. The pound was up near three-month highs against the dollar at $1.6107.Mr Snow's remarks were echoed yesterday by Kathleen Cooper, the Under-Secretary of Commerce for Economic Affairs, who said the dollar's 21 per cent drop over the past year had given exporters "somewhat more pricing power". Both continued to stress the US's commitment to a strong dollar policy.The rise in the euro poses a threat to the weak eurozone economy in the form of falling exports and rising import prices. The G10 bankers expect growth in the eurozone of less than 1 per cent this year, recovering to 2 to 2.5 per cent in 2004. They saw economic growth in the US reaching 3 per cent or more this year and continuing at trend over the next couple of years, Sir Edward said.He said: "The uncertainties associated with the Iraq war are not totally removed but have largely disappeared.