Nigel Farage accused Gordon Brown of mounting a smear campaign after the former prime minister demanded an urgent investigation into Brexit Party funding.
Mr Brown questioned whether sufficient safeguards are in place to protect against “dirty money” donated by foreign actors attempting to influence UK politics.
The ex-Labour leader was using a speech in Glasgow to warn that “American and Russian techniques of election manipulation” could be being “imported” to the UK.
Mr Brown has written to the Electoral Commission calling for an investigation into the Brexit Party’s finances.
But Mr Farage accused the former premier of an “absolutely disgusting smear” against his party.
“This from the man who was part of a Labour Party who, through Lord Levy, were making a lot of big donors members of the House of Lords,” Mr Farage said on a campaign visit to Exeter.
“How dare he? Most of our money has been raised by people giving £25 to become registered supporters and nearly 110,000 of them now have done that.
“Frankly, this smacks of jealousy because the other parties simply can’t do this.
“How open can we be? What you have got here are the conspiracy theorists doing their utmost to try and delegitimise what is the fastest-growing political movement this country has ever seen.”
Mr Brown will say: “I have written to the Electoral Commission, who have a duty to monitor every UK party’s election finance and spending, demanding Nigel Farage and the Brexit Party be investigated, and I am asking the European Parliament to investigate his failure to declare income where there are potential conflicts of interest.”
Mr Brown is expected to attack Mr Farage’s party for possible “under-the-counter and underhand” campaign financing ahead of the European elections on Thursday, when the Brexit Party is expected to sweep up the largest amount of votes.
He will highlight that the electoral watchdog had “warned of the dangers” of large amounts of cash being funnelled to parties in multiple small donations and linked this to the Brexit Party’s funding model.
And the former Labour MP will say he believes that, far from protecting democracy, Mr Farage’s party could be used to “fatally undermine … the heart of our democratic system”.
It would be simple for a foreign power or individual to fund @brexitparty_uk by paying hundreds or thousands of £499 in sterling or other currencies as the party does not even verify names. Our democracy is basically up for sale.
— Chris Bryant (@RhonddaBryant) May 20, 2019
Mr Brown will say Mr Farage heads a party “which is making questionable claims about the true source of its funding at a time when the Electoral Commission has warned of the dangers of multiple, small, anonymous donations being a cover for dirty money”.
Pro-EU Labour MP Chris Bryant also raised concerns, saying: “It would be simple for a foreign power or individual to fund (the Brexit Party) by paying hundreds or thousands of £499 in sterling or other currencies as the party does not even verify names.
“Our democracy is basically up for sale.”
Brexit Party chairman Richard Tice was asked on BBC Radio 4’s Today programme about the concerns raised by Mr Brown.
Asked if the Brexit Party was taking “under-the-counter, underhand” donations, Mr Tice said: “This really is utterly ridiculous.
“People are just jealous of our success and the fact we’re on course to win these elections.
“We’ve got a PayPal account for people paying less than £500; above that we apply the appropriate Electoral Commission rules.”
Asked whether he had just confirmed that the party did take cash from foreign citizens, Mr Tice said: “I don’t sit in front of the PayPal account all day so I don’t know what currencies people are paying in, but, as I understand it, the PayPal takes it in sterling.”
Critics claim the PayPal model is open to abuse because it does not require detailed personal information about donors, which other UK parties collect.
However, the Press Association understands that the law currently does not recognise sums of less than £500 given to parties as official donations, so rules on identification do not apply.
An official donation of £500 or more must be given by a “permissible donor”, who should either be somebody listed on the UK electoral roll or a business registered at Companies House and operating in the UK.
A spokesman for the Electoral Commission said: “The Brexit Party, like all registered political parties, has to comply with laws that require any donation it accepts of over £500 to be from a permissible source.
“It is also subject to rules for reporting donations, loans, campaign spending and end-of-year accounts.
“These rules are in place to ensure fairness and transparency of all political party finance.
“As part of our active oversight and regulation of these rules, we talk regularly to parties, including the Brexit Party, about ensuring they have robust systems in place so that they comply with the law.
“If we see evidence to suggest the rules have been broken, we will consider it in line with our enforcement policy.”