US billionaire George Soros foundation donated over £400,000 to reverse the Brexit vote, The Guardian reported.
The business magnate is the founder of the Open Society Foundation (OSF), and made over £1 billion betting against the pound on Black Wednesday, which forced the UK government to pull it from the European exchange rate mechanism.
The Best for Britain campaign which favours remaining in the EU, rather than fighting for a soft Brexit, has received the six-figure sum from OSF since the June 2017 election, The Guardian reported citing sources.
Lord Malloch-Brown, a former UK government minister and deputy UN secretary general, chairs the Best for Britain campaign, co-founded by Gina Miller, who took the UK government to court over the triggering of the Article 50 process to leave the EU.
Malloch-Brown said the campaign group had followed all rules and regulations governing financial contribution. ''We, like millions of people, believe that Britain should lead, not leave, Europe,'' he said.
''We work with campaigners, businesses, unions, politicians and community groups to make sure everyone has a strong campaigning voice,'' he said.
According secret analysis, hard Brexit would cost public finances £80 billion.
Meanwhile, free trade deals with non-EU countries would add less than 1 per cent to the long-term growth of the UK economy, The Times reported citing a leaked government analysis of Brexit.
According to economists, the benefits from boosting trade with non-EU countries would not offset the slower growth forecast under every form of Brexit. Growth could be about 5 per cent less by 2033-34 than forecast at present if any deal resembled the free trade agreement with Canada.
According to commentators, the best possible trade deal between the UK and US would provide around half of any gain from all non-EU deals, which would increase pressure on Theresa May to strike an agreement with Donald Trump as quickly as possible after Britain leaves the EU.