Enterprise tsar Lord Sugar has donated £400,000 to the Labour Party, he announced today.
The Labour peer said he gave the boost to the party's coffers to assist with its running costs during the General Election campaign.
Lord Sugar, star of BBC show The Apprentice, said he had donated cash during previous campaigns.
In a statement released to the Press Association, he said: "I can confirm that I have today agreed a donation of £400,000 to the Labour Party.
"When I have made political donations in the past, I have always done so at the time of a general election to assist in campaign running costs.
"I adopted this policy in 1997 and 2001 and am doing the same again this time."
The donation is the biggest the peer has made since he gave £200,000 in 2001 and £150,000 in 1997.
Labour welcomed the donation, which will be a boost to Prime Minister Gordon Brown as the party trails in the polls.
Business Secretary Lord Mandelson said: "Lord Sugar has announced he is making a donation of £400,000 as he has done in previous elections.
"Lord Sugar is a great example and a powerful voice for British enterprise and the values of hard work and I'm very pleased that, as in 1997 and 2001, he has again chosen to show his support for Labour and our vision of a future fair for all at this General Election.
"Lord Sugar's kind donation will help Labour candidates across the country make that case for Britain and for British business. We are grateful for his support."
With more than three weeks to go to polling day, Lord Sugar's donation will make a significant difference to Labour as it can be used to pay for staff and poster advertising campaigns.
The donation came on the day the Tories pledged to end the "big donor era".
In its manifesto, the party said: "The public are concerned about the influence of money on politics, whether it is from the trade unions, individuals, or the lobbying industry.
"We will seek an agreement on a comprehensive package of reform that will encourage individual donations and include an across-the-board cap on donations.
"This will mark the end of the big donor era and the problems it has sometimes entailed."