The UK Independence Party had a five-fold rise in donations in the run-up to this June's European elections.
Much of UKIP's donations were for the poster campaign
Most of the £1.2m - more than the Lib Dems received - came from Yorkshire businessman Paul Sykes' firm, which spent £715,000 on adverts.
Labour and the Tories also saw their donations rise in the second three months of this year.
As plans for the general election hot up, Labour's total rose to £4.4m and the Tories' to £3.6m.
Liberal Democrat donations slipped slightly to £925,000, according to the latest Electoral Commission registers.
The second quarter figures show donations to the British National Party fell to £15,870 from £26,014.
The Green Party meanwhile boosted its coffers by £83,435, up from £36,646 in the previous period.
UKIP's poster campaign helped it take third place in the European elections, doubling its share of the vote to 16% as former chat show host Robert Kilroy-Silk joined its MEPs.
The vast bulk of its donations were not paid in cash, for example Mr Sykes' Highstone Group property company paid for items such as the billboard sites and other election material.
Labour's total was up from £2.5m in the first three months of the year, when the Tories raised £2.6m and the Lib Dems £947,262.
The biggest Labour donation was the £505,000 from Lord Paul Drayson, who as the founder of Powderject faced controversy when his company was awarded a government contract to supply a smallpox vaccine.
But more than £3m of Labour donations came from the trade unions.
The latest figures also show a major rise in donations for anti-abortion group Prolife, up from £7,100 to £43,929.
They show a record 18 parties reporting donations, a reflection of the myriad of parties which put up candidates in the local, European and London mayoral elections.
Among the new parties were former Labour MP George Galloway's Respect - which received £13,000 in donations and the Christian Peoples' Alliance with £15,000.
The Electoral Commission is due to publish a review of party funding next month.
Lib Dem campaigns director Lord Rennard said there should be a cap on donations.
"No one person should be able to exercise
disproportionate influence as a result of extraordinarily large donations," he said.
"In a democracy, millions of pounds should not be more important than millions of votes."
The New Politics Network is among those campaigning for the reform.
Its director, Peter Facey, said there should be a cap on individual donations as well as new ways to reinvigorate grass roots activity.
"The one clear message from this latest donations report is that UK political parties are in the thrall of the few, not the many," he said.
"A single donor can transform the fortunes of a political party overnight, as we have seen in the case of Paul Sykes and UKIP.
"Even the larger parties depend on relatively few donors."