Labour lost another 25,000 members in 2022, putting it 125,000 down on its numbers at the last election, its newly published accounts show.
Keir Starmer's opposition however outstripped the Conservatives in donations, raising £47.2 million and returning to a surplus after running a deficit in 2021.
The Conservatives meanwhile lost £2.3 million in 2022 during what the party's annual accounts described as a "turbulent year".
The governing party's accounts, published by the Electoral Commission on Thursday, say the lower level of income, at £30.6 million, is partly due to "donor pledges moving into 2023".
Both parties are trying to woo donors ahead of an elected general election next year, when donations traditionally ramp up in the run-up to the campaign.
Labour had 407,445 members at the end of 2022, down from 432,213 the year before and 532,046 at the 2019 general election.
The party's recent peak of membership was 564,443 at the end of 2017, falling to 518,659 in 2018.
The Conservatives do not publish regular membership figures, but the central's party's income from membership fees was broadly flat at £1.97 million in 2022, down from £1.99 million in 2021.
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Show all 50The House of Commons Library recently cited an estimated figure of 172,000 Tory members as of September 2022.
Labour’s income in 2022 was £47.17 million and its expenditure £44.45 million, while the Tories raised £30.26 million against a spend of £33.06 million.
A Labour spokesperson said: “Thanks to Keir Starmer’s leadership, the Labour Party saw significant financial growth throughout 2022, and our finances have gone from strength to strength this year as we set out our five missions to transform Britain.
“The Labour Party is a changed party that is serious about getting into government and building a better Britain.”
In 2022 Liberal Democrats recorded total income of £5.95 million and expenditure of £6.69 million, a deficit, while the Scottish National Party had an income of £4.25 million and expenditure of £5.05 million.
