Three of Britain's leading businessmen refused to sign a letter endorsing Tony Blair because of the invasion of Iraq.
The three - Sir Terence Conran, Tim Waterstone and David Potter, the chairman of Psion - are long-standing Labour supporters and each of them signed a letter backing the party before the 1997 and 2001 elections.
But they refused to sign a round-robin letter extolling Labour's economic record which appeared in the Financial Times yesterday because they opposed the war and the way Britain was led into it on a false premise.
Mr Waterstone, the founder of Waterstone's bookshops, said: "For me it was the single issue of Iraq. The invasion was a totally shameful and disgraceful action. I think Blair should have resigned over Iraq and Gordon Brown should now be Prime Minister."
He added that he had not decided which way to vote next week even though he had supported Labour since his boyhood. "It is a sad moment for me because it has been my party since I was a child. But I am really horrified by Iraq and it just gets worse and worse."
Mr Potter, who founded the hand-held computer firm Psion 25 years ago, said the Iraq invasion had undermined his trust in Mr Blair and raised questions over the judgement of the Prime Minister and the Cabinet.
A spokesman for Sir Terence, whose business empire stretches from restaurants to shops, said he had disagreed with Mr Blair on a few things, particularly Iraq and university tuition fees. Last year, he also voiced his concerns over increasingly widespread smoking bans.
The three businessmen were among 58 executives who signed a letter in the Financial Times in 2001, endorsing Labour. This year, a total of 63 business leaders signed a similar letter, which hailed Labour's "unprecedented growth".
Other business leaders who refused to sign the letter this year despite their support in 2001 include Allan Leighton, the chairman of Royal Mail, and Sir John Parker, chairman of National Grid Transco.