ANTI-Brexit campaigners have called for Britain’s withdrawal from the EU to be "put on hold" after a criminal investigation was launched into allegations of illegal funding of the Leave campaign in the 2016 referendum, involving more than £8 million.

They also claimed that the investigation into the high-profile Leave campaigner Arron Banks for "suspected criminal offences" made the call for a People’s Vote unanswerable.

The probe has been launched by the National Crime Agency after the elections watchdog, the Electoral Commission, said it had reasonable grounds to suspect Mr Banks was not the true source of £8m of loans made during the campaign.

No mention was made of any Russian money or interference in the campaign.

Mr Banks, who co-founded Leave.EU, said he was confident the investigation would "put an end to the ludicrous allegations" against him and appeared unfazed by the allegations as he enjoyed a fishing trip in Bermuda.

The 52-year-old businessman, who wrote a book called The Bad Boys of Brexit, courted controversy for meeting Russian officials during the referendum campaign and being hosted at the Russian embassy.

He claimed the Commission's decision to refer him to the NCA was the result of "intense political pressure from anti-Brexit supporters".

Mr Banks added: "There is no evidence of any wrongdoing from the companies I own. I am a UK taxpayer and I have never received any foreign donations. The Electoral Commission has produced no evidence to the contrary.”

But Labour’s David Lammy tweeted: “We already know electoral law was broken. Now Arron Banks is under investigation because http://Leave.EU stands accused of spending foreign money.

“Brexit must be put on hold until we know the extent of these crimes against our democracy,” added the London MP.

Fellow Remainer, the Liberal Democrats’ Sir Edward Davey, also took to social media to say Mr Banks had "lied & cheated to damage my country & our futures. Surely even Conservatives must see the strong case for a People’s Vote on the deal has just become unanswerable”.

Labour peer Lord Adonis noted: “Latest Arron Banks & Vote Leave scandal reinforces case for a public enquiry into Brexit. Will also need to investigate behaviour of ministers, civil servants & the BBC.”

In contrast, MEP Gerald Batten, the Ukip leader, said: “The Remain campaign massively outspent Leave. They had the political, media, & international establishment on their side. Obama made a special trip in order to threaten us and tell us how to vote. Remain still lost. But they haven’t given up yet.”

The Commission also referred Leave.EU, its chief executive, Elizabeth Bilney, and the organisation that ran it, Better for the Country, to the NCA after carrying out a review.

Ms Bilney told the BBC that the Commission had consistently taken “a biased approach”, saying this was owing to its previous funding from the EU.

Some critics of Mr Banks have speculated whether his business links with Russia could be connected to the referendum campaign funding.

Earlier this year, the former Ukip donor was criticised by the Commons Digital, Culture, Media and Sport Committee for seeming to "want to hide the extent of his contacts with Russia".

But Ms Bilney rejected any Russian connection, saying: “I can confirm it wouldn’t have come from Russia…I run the group companies where the money was from and we don’t have any transactions that are from Russia.”

She added: "I am completely comfortable that we have done everything above board."

Detectives are looking at £2m supposedly loaned to Better For The Country by Mr Banks and his group of insurance companies.

They are also investigating a further £6m reported to have been given to the organisation on behalf of Leave.EU by Mr Banks.

Bob Posner, the Commission's Director of Political Finance, explained: "We have reasonable grounds to suspect money given to Better for the Country came from impermissible sources and that Mr Banks and Ms Bilney, the responsible person for Leave.EU, knowingly concealed the true circumstances under which this money was provided.

"This is significant because at least £2.9m of this money was used to fund referendum spending and donations during the regulated period of the EU referendum.

"Our investigation has unveiled evidence that suggests criminal offences have been committed which fall beyond the remit of the Commission. This is why we have handed our evidence to the NCA to allow them to investigate and take any appropriate law enforcement action. This is now a criminal investigation.”