Ukip faces questions over its finances after it was late reporting £63,000 ($94,809) of donations, according to the Electoral Commission.
The independent watchdog said on 23 April that the non-cash donations were not filed by the 12 April deadline. The donations came from Bristol-based insurance firm Rock Services Ltd.
Multi-millionaire businessman Arron Banks, a director at the firm, switched his support from the Tories to Nigel Farage's party last year.
The Commission said that political parties must submit weekly donation and loan reports to the watchdog if they are standing candidates in the UK parliamentary election and have received any donations or loans exceeding £7,500.
"These should have been reported to the Electoral Commission in their first weekly pre-poll report. The Commission is in correspondence with the party to establish the reasons for this," the organisation added.
The watchdog also revealed that £1,660,458 in donations to four registered political parties in Great Britain was reported for the week starting 6 April.
The Commission said that Labour reported the greatest number of donations over £7,500, totalling £1.1m.
Most of the donations (£737,946) came from trade unions aligned with Ed Miliband's party, including the Transport Salaried Staff Association (TSSA), Unison and Unite.
The Tories registered less than half of that amount with £492,512 and the Liberal Democrats drummed up £50,000. Finally, Ukip pulled in £8,000.
The Commission revealed that, between 30 March and 12 April, the political parties received £4.1m in donations.
Labour had attracted almost £3m (£2,997,258) and the Tories had recorded £994,362 worth of donations over the period.
The Greens had only registered £8,400 worth of donations, below the £13,792 for the Co-operative Party.
The figures come with just two weeks to go before the general election on 7 May, with Labour one point ahead of the Tories (34% v 33%) in the latest opinion poll from YouGov.
Ukip had not responded to a request for comment at the time of publication.