A leading member of the UK Independence party, which has railed against the European "gravy train", has demanded its MEPs contribute £10,000 each from their parliamentary allowances and salaries towards the costs of the party's British headquarters or risk being deselected.

Alan Bown, a party donor who sits on its national executive committee, wrote to Ukip representatives in Brussels in 2011 suggesting they should be "good value for money" and divert EU cash to the party's headquarters or face the sack, according to leaked documents. He pointedly added that thousands of pounds of EU allowances could be claimed without submitting receipts.

Party leader Nigel Farage and the party's national executive committee subsequently put pressure on the MEPs to pay more to support the running of the party, sources said. Ukip sources say MEPs are still placed under "immense pressure" to contribute to the party.

Bown's proposals prompted a furious response from the party's MEPs, who feared they would be at risk of breaking the law if they diverted funds. Another leaked email shows that the party's immigration spokesman, Gerard Batten, warned Ukip officials that he and other MEPs could face jail if they carried out Bown's demands.

The disclosures are confirmation that the party's MEPs have been under increasing pressure to divert their allowances into the party's UK operations, in breach of EU rules.

EU documents state that allowances "are only eligible when spent on activities and objects which are directly linked to the office of a member of the European parliament". Bown, a former bookmaker, sent an email to national executive members in January 2011 with an attached document titled "MEPs' Financial Contributions to the Party".

He complained that MEPs had failed to contribute to the party and pointed out that it costs £125,000 to get each of them elected, questioning whether they were good value for money.

Arguing that the party's headquarters, Lexdrum House in Devon, spends a lot of money getting MEPs elected, he added: "In my opinion the MEPs have a clear duty to help finance Lexdrum House."

The email points out that to get on a Ukip selection list, MEP candidates have to sign a "code of conduct" document complying with Bown's demand that MEPs "provide substantial financial support to the central party out of income".

A version of the code of conduct from 2008 has been leaked to the Guardian. It says the party's MEPs pledge to "submit to oversight and act on advice from the party regarding the use of parliament allowances and expenses".

In his email, Bown, 71, says: "Most MEPs draw a salary of £80K+ per year plus generous expenses of approximately £320K some of which does not require receipts."

He said he had spoken to fellow Ukip peer and former party leader Lord Pearson and suggested he had agreed that this year's reselected candidates should be judged in part on their payments to the party.

"Before an MEP is allowed to stand for re-election for 2014, the NEC should look at their record over the previous 5 years to see what he or she had achieved and particularly their financial contributions to the party.

"The NEC reserves the right to blackball any MEP from standing again if their record was poor."

Bown's email prompted an angry response from a number of MEPs, insiders said. A few days later, Batten, who has called for Muslims in Britain to sign a pledge of allegiance, sent an email claiming that following Bown's advice would risk a criminal record and jail.

"The staff and office allowance combined is £253k," said Batten. "This money can only be spent according to the rules on staff and offices. Only £42k of that does not require 'receipts'. To use it for personal or political purposes is against the rules. Are you suggesting we should use it illegally? Are you suggesting we should risk prison to help the party financially?"

Two weeks after the email exchange, some MEPs met Bown, Farage and Stuart Wheeler at the Farmers Club in Whitehall, where they were informed that they were each under pressure to increase contributions to the party.

The party argues the EU is a waste of money and calls for Britain's withdrawal.

It comes amid concern that the party's rapid growth in popularity and expensive European parliament election campaign is not being supported by a corresponding rise in income.

It was reported by the Times on Saturday that the EU authorities have been asked to investigate whether some of Ukip's staff in the UK are being paid from EU money, in breach of regulations.

The disclosures will prove embarrassing for the party as it tries to portray itself as a realistic and influential political force. Some party officials have privately voiced concern that money pledged by Paul Sykes, the former Tory donor, has not come through when they need to fund the European election campaign. Neil Hamilton, the former Tory MP, told the Observer this month: ""So far we haven't seen the colour of his money."

Ukip has come under increasing scrutiny over its alleged misuse of EU expenses. Tom Wise, the party's former MEP for East of England, was jailed for expenses fraud after paying himself £36,000.

Two of the party's senior members have repaid more than £37,000 meant for office staff after diverting it to party workers based in the UK.

Nikki Sinclaire, MEP for the West Midlands, told the Guardian last year that Farage told her the party would not be able to gain access to extra funds meant for a new political grouping without her support.

The party denied her claims.

Batten told the Guardian on Friday that he has never broken the rules.

"My donations to the party are made out of my personal income," he said. Ukip said: "Alan Bown is an extremely generous donor to Ukip and is one of 16 members of the party's NEC. He is well known for seeking to encourage other members of the party including MEPs to seek to emulate his own outstanding levels of generosity. All of our MEPs conduct their financial affairs honestly and comply with the rules covering allowances and expenses. Any donations they make to the party come from their post-tax salaries."

Bown is in the US and did not respond to requests for a comment.