Donations to the Labour Party continue to outstrip those to the Conservatives, according to Electoral Commission figures for April to June.
Twenty parties received £14m in donations between April and June
The Conservatives received individual donations of £4.6m - below Labour's £5m - but also got £1.7m of public money for policy development.
Labour was in debt by £20.2m as of 30 June, with the Conservatives borrowing £16.3m, and Liberal Democrats £1m.
In total 20 parties got £14m donations bringing the year's tally to £25m.
Labour, which does not receive public money because it is in government, was given slightly more from donors compared with the previous quarter, when it received £4.99m.
Significant donations came from Iranian millionaire Mahmoud Khayami, who gave £500,000, and Muslim Friends of Labour gave £300,000.
The party also received £250,000 each from millionaire Jon Aisbitt, financier Ronald Cohen, a friend and confidant of prime minister Gordon Brown, and Nigel Doughty.
A Labour spokesman said: "Our finances remain in a challenging position but the upturn of recent months continues to be reflected in the figures from the Electoral Commission.
"Donations to the end of June 2007 show an increase of £3.6 million on the same stage in 2006."
The Conservatives' biggest donors were Edinburgh grain merchants Philip Wilson (Grain) Ltd, who gave £300,000, followed by £287,898 from Harris Ventures Ltd, whose chairman is the Conservative peer and businessman Lord Harris of Peckham, and £250,000 from developers Gallagher UK Ltd.
Party chairman Caroline Spelman said: "Under David Cameron the Conservative Party is widening its support at base and raising more funds from a broader number of donors.
"We are more than ready to fight a general election."
The Liberal Democrats received £1.3m in donations, which included at least £500,000 from public funds.
The UK Independence Party received £84,400, and the Scottish National Party got £623,600.
Peter Facey, director of campaign group Unlock Democracy, said: "It is clear that the major parties are struggling to pay of their debts.
"In 2004, roughly 75% of major donations went to central Labour and Conservative coffers.
"Over the past 12 months, this proportion has increased to 90%.
"This centralisation of party politics can only lead to even less activity at a grassroots level."