Arron Banks, the biggest financial donor to the Leave campaign, has suggested the German Chancellor Angela Merkel "might as well have" driven the lorry used in the Berlin market attack because of her policy on accepting refugees.

The prominent Ukip funder said he was “fed up with diplomacy” on Twitter and defended the party's former leader Nigel Farage after he suggested the widower of murdered Labour MP Jo Cox supported extremism.

He wrote: “Farage rightly pointed out that terrorists would flood in with so-called refugees. He was right as in so many other things.

“I blame unlimited immigration without integration and the soft liberals like yourself that don't have the courage to call it what it is.”

His use of the word "flood" prompted comparisons to Enoch Powell's Rivers of Blood speech. "Merkel did not drive the lorry," added one response.

The insurance tycoon, who invested £7.5 million into the successful Brexit campaign, replied: "She might as well have."

Mr Farage was criticised by Brendan Cox, the husband of murdered MP Jo Cox, for “blaming politicians for the actions of extremists” by claiming the lorry attack, which killed 12 and injured dozens more was “no surprise” and would form part of Ms Merkel’s legacy.

“Of course, he would know more about extremists than me, Mr Cox. He backs organisations like Hope Not Hate, who masquerade as being lovely and peaceful, but actually pursue violent and undemocratic means,” Mr Farage told LBC radio.

Hope Not Hate said it was consulting with its legal team over Mr Farage’s “serious and potentially libellous statement”.

“We have no idea on what Mr Farage bases his outrageous comments," a spokesperson said. "Hope not hate has a proud history of campaigning against extremism and hatred.

“We will not be making any further comment until we have had the opportunity to consult with our lawyers.”