Nigel Farage could be in trouble with the elections watchdog after failing to declare £200,000 in donations over more than a decade.
The Ukip leader apparently disclosed to Brussels authorities that he had been receiving free use of an office in Britain since 2001 - but did not tell the Electoral Commission. This re-opens questions about whether Mr Farage has been pocketing EU expenses.
The issue is said to have emerged only when officials saw the office - a former farm grain store - mentioned in news stories in the run-up to recent local and European polls.
Under the Political Parties, Elections and Referendums Act 2000, regulated recipients - including MEPs like Mr Farage - must report gifts within 30 days of accepting them.
Penalties for not complying can include fines of up to £20,000 and, in the most extreme cases, a 12-month prison term.
"When we became aware of the potential unreported donations, we were in correspondence with Mr Farage," a spokeswoman for the commission said.
"This then led to the donations being reported to us.
"We have not yet made a decision about whether any further action will be taken against Mr Farage for reporting the donations late.
"We are continuing to review all of the necessary information supplied to us by Mr Farage and are considering it carefully."
A Ukip spokesman said: "Every year since 2001, Mr Farage has declared in his European Parliament Register of Interests the use of a rent-free office from J Longhurst Ltd.
"The premises has been used as his MEP office so the European Parliamentary register was the logical place for it to be declared.
"Mr Farage was surprised to learn that the Electoral Commission thought it should be informed as well, as this did not accord with the professional advice he had received at the time."
Ukip faced more embarrassment over donations in recent months, after it emerged the party was continuing to receive money from Demetri Marchessini - who thinks it is acceptable for a husband to rape his wife, that homosexuality is a sin and that women should not be allowed to wear trousers.
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The Times previously raised questions about why Mr Farage was receiving £15,000 a year in MEP allowances to run a constituency office when he was not being asked to pay any rent on the converted grain store in Bognor Regis.
Mr Farage has insisted it is up to him how the money is used, and denied any wrongdoing or personal profit.
Details released by the commission show he declared 14 benefit-in-kind donations from Mr Longhurst on May 16, dating back to 2001 and totalling around £205,000.
The fresh embarrassment for Ukip came as controversial former Ukip MEP Godfrey Bloom yesterday said that Mr Farage should be "a little more circumspect" about his closeness to women.
He said the Ukip leader needed to be more cautious after he was last week photographed returning to his hotel with a woman at 3am.\
Mr Bloom who resigned from the party last year after a number of controversies, told the BBC’s Daily Politics: "I think perhaps if I was his old dad I’d say be a little more circumspect, but that’s the pot calling the kettle black with me."