Billionaire George Soros was today told to 'butt out' of UK affairs after it was revealed he had pumped £400,000 into a campaign fighting to stop Brexit.

Tory backbench Brexiteer Henry Smith said 'serious questions' must be asked into why a US citizen was allowed to pump the cash into a UK political campaign.

And he said Mr Soros - who is known as the 'man who broke the Bank of England' after he bet against the pound on black Wednesday -is 'no friend of Britain's'.

The US investment mogul was revealed today to be one of the biggest donors behind the Best For Britain group, launched by ardent Remainer Gina Miller.

The scale of the financial backing has fuelled fears the process of leaving the EU could be watered down or even halted altogether.

Mr Smith, Tory MP for Crawley, told Mail Online: 'Soros has never been a friend of Britain’s best interests. As a US citizen he should butt out of telling the UK they should remain under Brussels’ yoke.

'Serious questions need to be asked as to how a foreign national can be funding a British political campaign.'

Billionaire investor George Soros, pictured in Brussels last year, is said to have handed £400,000 to a campaign arguing against Brexit

Gina Miller, the millionaire businesswoman who took the Government to court over Brexit, promised 'the biggest tactical voting effort in our history' when she launched the Best for Britain campaign in April last year

Former Ukip leader Nigel Farage said people were starting to 'wake up' to the danger of the referendum vote being reversed.

Ms Miller, who stopped working with Best for Britain after the election in June, also urged the organisation to be more 'transparent' about who was funding it.

The news emerged as Theresa May gathered her Brexit war Cabinet amid fears ministers are deadlocked over what 'end state' they want from negotiation with the EU.

Who is George Soros and why is he known as the man who broke the Bank of England? George Soros had already made a fortune and a formidable reputation by 1992. But that was when he secured his tag as the 'man who broke the Bank of England'. Short selling US$10billion worth of Sterling during the Black Wednesday crisis made him a reported profit of £1.5billion. The 87-year-old Hungarian-born financier is now one of the world's richest men. His wealth was estimated by Forbes magazine last year at £25billion. Mr Soros has previously warned that Brexit will be a disaster for the economy, and suggested the UK could immediately apply to rejoin the EU. One of Mr Soros's foundations gave the money to Best for Britain, a Remain group that wants to force a second EU referendum. Over the past 40 years he is said to have donated £11billion to philanthropic causes. Advertisement

Downing Street insisted that the UK will be leaving the bloc in March next year regardless of the growing clamour from Remainers.

Mr Soros has previously warned that Brexit will be a disaster for the economy, and suggested the UK could immediately apply to rejoin the EU.

The 87-year-old Hungarian-born financier is one of the world's richest men who made a reported £1.5 billion betting against sterling on Black Wednesday in 1992.

One of Mr Soros's foundations gave the money to Best for Britain, a Remain group that wants to force a second EU referendum.

Ms Miller, the millionaire businesswoman who took the Government to court over Brexit, promised 'the biggest tactical voting effort in our history' when she launched the Best for Britain campaign in April last year.

The project was set up in office space provided by Sir Richard Branson, who gave it some £25,000 to help it launch.

According to the Telegraph, businessman Stephen Peel and Sir Martin Sorrell, the chief executive of advertising firm WPP, attended a dinner with Mr Soros last week.

Best for Britain chairman Lord Malloch-Brown, a former minister and diplomat, said the group had followed rules governing financial contributions 'to the letter'.

Former Ukip leader Nigel Farage said people were starting to 'wake up' to the danger of the referendum vote being reversed

He said: 'We have never hidden our agenda; we have been campaigning hard to win a meaningful vote on Brexit, which we did, and to keep all options on the table, including staying in the European Union.

How could a second Brexit referendum be called and what are the chances of there being one? Hard-core Remainers have called for a second referendum on Brexit - but the chances of one happening before we quit the EU are slim. For a referendum to be held it has to be called by the Government, and the result of the vote is advisory and not legally binding. Theresa May wants to get the details of the two-year transition deal signed off next month and the final deal thrashed out in October this year. But even if this timeline is stuck to, it would only be the broad outline of a deal that was agreed - not the fine detail. Some Remainers say that this deal should then be put to a second referendum - allowing the public to vote on what kind of Brexit they want. But the Government has pointed out this risks seriously undermining their negotiating hand as Brussels would know any detail could be easily vetoed by voters. Most MPs are against having a second referendum with Labour coming out against it. Instead Jeremy Corbyn's team want MPs to have a 'meaningful vote' on the deal - with the option of send the PM and her minsters back to the negotiating table. Advertisement

'We, like millions of people, believe that Britain should lead, not leave Europe. We work with campaigners, businesses, unions, politicians and community groups to make sure everyone has a strong campaigning voice.

'George Soros's foundations have, along with a number of other major donors, also made significant contributions to our work.

'Indeed through his foundations he has contributed £400,000.

'But our small donors have collectively contributed more and the commitments of the other major donors also exceed this amount.

'So he is an important and valued donor but his funding is one amongst many sources.'

In a statement, Ms Miller said she had not been involved in Best for Britain since June.

'One of the greatest failures, and sadnesses, of the whole Brexit era has been the lack of transparency about key players' motivations, agendas and activities and incompleteness of information that is placed in the public domain,' she said.

'I encourage Best for Britain, and all those keen to play their part in the Brexit debate to be open and honest about what they stand for, whom they represent and by whom they are funded.'

Speaking on ITV's GMB programme today, Mr Farage said there was a real threat to the Brexit process, and Remainers were exploiting fears about the economy.

'All that's happened today is that a few people have started to wake up to it,' he said.

'The referendum wasn't about an economic deal. It wasn't about projecting that in 15 years time will we be richer or poorer? The referendum was about leaving the political union and becoming an independent self-governing nation.'

Mr Farage also said he thought Theresa May was struggling to get traction in negotiations with the EU.

'I'm very pessimistic about the deal she is going to get. I want to be an independent country,' he said.

Best for Britain chairman Lord Malloch-Brown, a former minister and diplomat, said the group had followed rules governing financial contributions 'to the letter'. Nick Timothy (right) claims Best for Britain want to bring down the Government

Boris Johnson, pictured in Downing Street ahead of the war Cabinet today, is urging a clean break from the EU

Attorney General Jeremy Wright was in Downing Street today ahead of the Cabinet subcommittee meeting. Defence Secretary Gavin Williamson is also a member of the group

A leaked Best for Britain strategy document proposed a nationwide campaign in the coming weeks to 'wake the country up and assert that Brexit is not a done deal, that it's not too late to stop Brexit'.

It also called for a series of Momentum-style mass rallies and concerts with a 'heavy youth focus'.

The document suggests the campaign aims to 'trigger a new referendum, or election' which the group will use to block Brexit altogether.

'We must prevail decisively so reassuring Europe that our return will be permanent,' it states.

WHO ARE BEST FOR BRITAIN AND WHAT DO THEY WANT? Best for Britain was launched by Gina Miller as a campaign to encourage tactical voting against Brexit Best for Britain is a campaign group dedicating to moderating and ultimately reversing Brexit. It was launched by Gina Miller, the former model who successfully challenged the Government in court over to Article 50, to encourage anti-Brexit tactical voting at the election. Ms Miller left the group soon after the election and former Labour minister Mark Malloch-Brown took over as chairman. The group is actively fundraising for its efforts to frustrate Brexit. As well as big money donations from people like George Soros, it run crowdfunding - including a new campaign to 'stand up for free speech'. It urged MPs to vote against the flagship Brexit Withdrawal Bill and campaigns to protect universities from what it describes as a right-wing witch hunt. The group draws cross party support, frequently issuing statements from MPs including Daniel Zeichner from Labour, Tom Brake from the Lib Dems and Green Caroline Lucas.. The board includes former Olympian Stephen Peel economist Anatole Kaletsky, businessman Clive Cowdery, while the CEO is activist Eloise Todd. Advertisement

The Prime Minister's latest meeting with her Brexit 'war Cabinet' comes as the government prepares for a crucial stage of talks with Brussels.

But there are signs that the sub-committee will again try to fudge choices over the thorniest issues like customs arrangements with the EU and the Irish border.

There is not thought to have been any breakthrough at yesterday's meeting.

It could be weeks until the full Cabinet thrashes out a stance that will be taken into the negotiation process with Brussels in March.

The Cabinet subcommittee - made up of Mrs May and her top ministers including Philip Hammond, Amber Rudd, Boris Johnson and Michael Gove - discussed the Ireland issue yesterday afternoon.

The talks also covered the potential immigration arrangements for after we leave - while today the group is considering future trade arrangements.

But there are deep tensions between the Brexiteer and Remain factions, with Mr Hammond accused of trying to keep the UK tied to the EU customs union for years after we formally leave the bloc.

The involvement of Mr Soros was revealed in a story written by Theresa May's former chief of staff Nick Timothy in the Telegraph.

Mr Timothy, who backed the Leave cause, used his column in the newspaper to claim that Best for Britain wanted to bring down Mrs May's government.

He wrote: 'The objective is to convince MPs to vote against the deal Theresa May negotiates with Brussels, regardless of its content and despite the risk that doing so could mean Britain leaves the EU with no alternative agreement in place.

'Malloch-Brown and his backers believe that, if Parliament rejects the Brexit deal, the Government will fall, and Brexit can then be stopped.'

He said it should be a 'wake-up call' to Conservatives in Parliament, adding: 'However Tory MPs feel about Brexit, voting against the Government when the deal is done risks something much, much worse.'

But Lord Malloch-Brown said: 'We think the British people deserve a final say on the Brexit deal and believe the country has been led down a dangerous false turn.

'This is a democratic and patriotic effort to recover our future and we welcome support for our efforts from many quarters.'

MailOnline has contacted Mr Soros's representatives for comment.

COULD REMAINERS DEPLOY MOMENTUM TACTICS TO FORCE BREXIT RETHINK? Best for Britain is planning to emulate Jeremy Corbyn support group Momentum to force a rethink on Brexit. A leaked strategy document proposed a nationwide campaign to 'wake the country up and assert that Brexit is not a done deal, that it's not too late to stop Brexit'. It also called for a series of Momentum-style mass rallies and concerts with a 'heavy youth focus'. The group wants to 'pressure' MPs in 100 Leave-supporting constituencies, and sets out how organisers 'have a range of guerrilla marketing tactics' to ratchet up the profile of Remain messages. The document suggests the campaign aims to 'trigger a new referendum, or election' which the group will use to block Brexit altogether. 'We must prevail decisively so reassuring Europe that our return will be permanent,' it stated. Advertisement

Mr Soros (pictured with EU commission President Jean-Claude Juncker in 2017), previously said it was possible that the UK would apply to rejoin the European Union soon after Brexit