They wrote to the Prime Minister as Leslie Silver, the former chairman of Leeds United Football Club, announced he had given Labour a pounds 25,000 donation.
The gift from Mr Silver, who made his fortune from paint manufacturing and is now on the Leeds United board, takes the total of individual donations by leading businessmen - several of them connected to football - to over pounds 6m.
The donations from business to Labour's war chest now rival the sums given to the party from its traditional backers - the trade unions. In calling for the Nolan inquiry, the Labour leader underlined he was relaxed about Tory allegations that he had concealed the accounts supporting his office and those of his deputy, John Prescott, and Gordon Brown, the shadow Chancellor.
The joint leaders' letter, also signed by David Trimble, the Ulster Unionist Party leader, and four other party chiefs said they had "serious doubts" about the sources of pounds 50 million in funds for the Tory Party.
Mr Silver, the latest in a series of substantial donors to be named by Labour, said: "I've always been a Labour supporter, but under Tony Blair, the party has transformed itself.
"He is an excellent leader and I think the team he is putting together for government will be dynamic and exciting and give this country a fresh start. I think you will find more and more people in business are coming over to Labour" he said.
Mr Silver's gift to Labour follows the pounds 1m pledged to the party by the late Matthew Harding, vice-chairman of Chelsea Football Club, who died last month in a helicopter accident.
Mr Harding was to have been on Labour's New Business Committee, established to secure new business contacts for the party. Labour named the members of its Business Committee as: film producer Sir David Puttnam; Alec Reed, chairman of the Reed Executive employment agency who is giving the party pounds 100,000; Chris Haskins, head of Northern Foods; and the millionaire Labour MP, Geoffrey Robinson.
It also named its new Election Campaign Fund Committee as: publishing millionaire Bob Gavron, who donated pounds 500,000 to the party; the film director and Labour peer, Lord Attenborough; music publisher Michael Levy; and the Labour party general secretary, Tom Sawyer.
Labour also disclosed on Thursday night that Pearson Television's chief executive Greg Dyke and Labour peer Lord Hollick, chief executive of United News and Media, which owns The Express, had each given the party between pounds 25,000 and pounds 50,000.Reuse content