Gordon Brown branded Nigel Farage a “man of the PayPal” yesterday as he demanded a full investigation into the controversial finances of the Brexiteer.

The former prime minister ridiculed the Brexit Party leader’s image as a “man of the people” on the day the right-wing figurehead had a milkshake thrown over him while campaigning in Newcastle.

Brown’s claims came after Farage boasted his newly-formed party was receiving more than £100,000 a day, as it soared to first place in the UK polls ahead of the European elections.

The Brexit Party allows donations of under £500 by PayPal on its website, prompting concern that it could be vulnerable to foreign influence.

Nigel Farage covered in milkshake while out campaigning in Newcastle

Brown challenged the Electoral Commission and the European Parliament to clarify before polling day on Thursday whether they have concerns over dubious payments.

Speaking to Labour supporters in Glasgow, he said: “The Electoral Commission and the European Parliament should now investigate the finances of Nigel Farage and the Brexit Party.

“Democracy is undermined when we have undeclared, unreported, untraceable payments being made to the Brexit Party.

“We have the potential for underhand and under-the-counter payments being made.”

Brown, the former Kirkcaldy and Cowdenbeath MP, pointed out that the there is already a criminal investigation into Farage’s Brexit campaign, Leave.EU, and its millionaire backer Arron Banks.

Farage is facing a separate investigation by European parliament authorities over claims that he failed to declare nearly half a million pounds in gifts from Banks.

The empty milkshake cup from Five Guys thought to have been emptied on Nigel Farage

Brown added: “This is a not a party in the ordinary sense, this is a private company.

“It’s run by Nigel Farage – donations go through PayPal and he’s not going to be remembered as he wants, as the man of the people.

“He’ll be remembered as the man of the PayPal, because that’s where the money’s coming from.”

Farage accused the former premier of an “absolutely disgusting smear” against his party and claimed it was rooted in “jealousy”.