Billionaire financier George Soros has pledged an additional £100,000 to support efforts to fight Brexit as donations flooded in to a group attempting to mobilise public opinion against withdrawal.

The investor's move comes after Mr Soros drew anger from Brexiteers last week when it was revealed he was donating £400,000 to the campaign group Best for Britain in an attempt to halt withdrawal from the EU.

The involvement of Mr Soros, who has an estimated net worth of $25.2bn (£18bn), making him the 29th richest person in the world according to Forbes, is understood to have emerged after he entertained six Conservative donors at his house in Chelsea.

But after a sustained attack, Mr Soros, through his Open Society Foundations (OFS), announced on Sunday he would match donations – to a maximum of £100,000 - given to the Best for Britain campaign.

The group’s crowdfunding page “your right to fight Brexit” has already raised over £70,000 since Thursday last week, with over 2,000 individuals donating to the cause.

The organisation says raising £75,000 will allow Best for Britain to campaign on social media and reach tens of thousands of new people.

Eloise Todd, the organisation’s CEO, said: “We live in a democracy, and the right to freedom of speech is precious. Elements of the right-wing press don’t seem to agree.

“The UK’s future with the EU is not a done deal, there is still a vote to come and people across the country deserve to know the truth about the options on the table: one of which is staying and leading in the EU.

“George Soros and his foundation is kindly offering to help match-fund to give Best for Britain more support so we can make sure this message gets out: the biggest decision on Brexit is yet to come.”

Mr Soros also told the Guardian: “I am happy to take the fight of those who have tried to use a smear campaign, not arguments, to prop up their failing case.”