Gordon Brown is fighting for his political life after the shock resignation of Work and Pensions Secretary James Purnell. Mr Purnell made has dramatical announcement as polls closed in the European and local council elections. In a resignation letter released to several newspapers, Mr Purnell called on Mr Brown to step aside for the good of the Labour Party, saying that his continued leadership makes a Conservative victory more, not less, likely. The letter reads: "Dear Gordon, We both love the Labour Party. I have worked for it for twenty years and you for far longer. We know we owe it everything and it owes us nothing. "I owe it to our Party to say what I believe no matter how hard that may be. I now believe your continued leadership makes a Conservative victory more, not less likely. "That would be disastrous for our country. This moment calls for stronger regulation, an active state, better public services, an open democracy. It calls for a Government that measures itself by how it treats the poorest in society. Those are our values, not David Cameron's." Downing Street said in a statement that Mr Brown was "disappointed" by the resignation but added that he will continue to give his undivided attention to addressing the challenges facing Britain. The leading Blairite is the third member of the Cabinet and fifth minister to announce his resignation in just three days, and the most senior Labour figure to call for Mr Brown to go. Conservative Party leader David Cameron reacted to the news by saying: "In a deep recession and a political crisis, we need a strong united Government. Instead we have a Government falling apart in front of our eyes. "For the sake of the country, Gordon Brown must carry out the one final act of authority left open to him, go to the Palace and call the general election we have been demanding." But Labour ministers have been rallying around the Prime Minister. Defence Secretary John Hutton - another leading Cabinet Blairite - said: "I am sorry that my good friend James Purnell has decided to resign. "I think he has made the wrong decision because I firmly believe that Gordon Brown is the right man to lead our party and our country. "I urge everyone in the party to remain united behind his leadership." And Europe minister Caroline Flint - who some at Westminster had expected to be the next to quit - has given the PM her backing. She said: "I am staying in the Government. I have spent my entire ministerial career for six years now serving Tony Blair and Gordon Brown, and I am very proud to be in a Labour Government and very proud to be part of Gordon Brown's Government."