A UKIP-dominated group has reportedly misspent almost half a million euros of EU funding on electioneering and to help boost the Brexit campaign, according to a leaked audit.
The party is accused of spending British taxpayers' cash, breaking European Union spending rules, on polling in key UKIP target constituencies ahead of the last UK general election and also ahead of the EU referendum.
According to Sky News, the money was provided to the European political grouping, the Alliance for Direct Democracy in Europe (ADDE), which is dominated by Nigel Farage's party.
The ADDE was created by Mr Farage two years ago and is made up of populist right wing and Eurosceptic MEPs, around half of whom are from UKIP.
The audit says ADDE financed polling in the UK between February and December last year, which has been judged as "indirect financing of a national political party" and "a referendum campaign" - both of which are prohibited by European Parliament rules.
The report concluded: "The constituencies selected for many of the polls underline that the polls underline that the polling were conducted in the interest of UKIP.
"Most of the constituencies can be identified as being essential for reaching a significant representation in the House of Commons from the 2015 General Election or for a positive result for the 'Leave campaign'."
And on the EU referendum the auditors said: "Several polling can be considered as financing of a referendum campaign which violates 8(4) ... prohibiting the financing of referenda campaigns."
The audit, drawn up for the European Parliament Bureau, puts the total misspend at over €500,615.55 by ADDE, which includes other parties in Europe, but a EU spokesperson said the "lion's share" was by UKIP, amounting to over €450,000.
A final decision by the European Parliament Bureau will be made on Monday.
If the bureau agrees with the conclusion of the external audit, UKIP could be forced to pay back more than €170,000 while not being able to claim hundreds of thousands more.
A spokesman for ADDE said they would be taking the matter to court and that the definition of "expenditure supporting a political party" had been changed.
He said: "The parliament administration has for months taken an aggressive and hostile attitude over the audit, amounting to nothing short of deliberate harassment.
"We have responded to their queries with a mass of information and explanation justifying our activities and expenditure. They have simply ignored our submissions and in several cases these submissions have been made repeatedly on their request."
