Labour outstripped the Tories in party fundraising over the summer by nearly 30%, the latest official figures show.
Donations registered with the Electoral Commission between July and September totalled £3,529,270 for the Opposition compared with the Conservatives' £2,744,618.
The third largest income during the period was recorded by the Scottish National Party, which received £1,988,657, the commission said.
It comes a day after the main Westminster parties united to oppose extra state funding for parties as part of a bid to end the reliance on a few wealthy donors.
The Commission's figures showed that taxpayers underwrote political parties to the tune of just under £2.1 million in the quarter.
Fears over the political impact of increasing that when voters were facing service cuts and economic uncertainty scuppered reform efforts yesterday.
A sleaze watchdog had suggested using an extra £23 million-a-year taxpayer subsidy to make up for imposing a £10,000 cap on donations and tighter rules on trade union funding.
Almost 90% of the Labour total - £3,138,443 - came from the unions. That figure is certain to fuel Tory claims that the party is overly influenced by the sector.
A Labour spokesman said that its biggest single source of income was membership subscriptions and small donations below the threshold requiring declaration to the commission.
The three main parties also came under fire from the watchdog for late reporting of some of their donations - with the Tories and Liberal Democrats also censured over loans reporting.
Outstanding loans now totalled £14,789,996, the Commission said.