Steel magnate - and Britain's richest man - Lakshmi Mittal has donated £2m to the Labour Party.
Mr Mittal is a longstanding Labour donor
Tony Blair said he was "delighted that Mr Mittal, who is one of the world's most successful businessmen, has made such a generous donation".
Mr Mittal, who according to the Sunday Times rich list has a £14.8bn fortune, is a longstanding Labour donor.
Labour admitted "acute cash flow problems" in November after figures revealed it owes £23.4m.
Speaking after Mr Mittal's donation was announced, a Labour spokesman said the money would "allow the party to continue to make investments to meet the electoral challenges we face over the next year".
Party chairman Hazel Blears also praised Mr Mittal for his "very generous donation".
Mr Mittal was not among those who bankrolled the 2005 election campaign, and there is no suggestion that he has sought any honours in return for his support for Labour.
In a statement, Mr Mittal said: "I am a long-term supporter of the Labour Party and the work it has done in the United Kingdom to improve the overall prosperity and prospects of the country since coming to office in 1997."
From modest beginnings in India, Mr Mittal has created a steel empire spanning the globe.