A Russian link to Boris Johnson and Michael Gove’s successful plot to persuade Theresa May to take a tougher stance on Brexit has been uncovered by The Mail on Sunday.

This newspaper has established that a secret letter sent by the Cabinet Ministers to the Prime Minister was co-ordinated by a senior figure in a free-market UK think-tank founded by a tycoon who made a fortune in Russia following the collapse of the Soviet Union.

The financier who established that think-tank, the Legatum Institute, also helped President Vladimir Putin’s associates to take control of Russia’s state energy giant Gazprom.

The institute’s economics director, Shanker Singham, was the ‘third man’ in drawing up Johnson and Gove’s Brexit ultimatum, which this newspaper disclosed last month.

The organisation, which operates from a townhouse in London’s affluent Mayfair, was set up using some of the fortune that secretive New Zealand-born tycoon Christopher Chandler made with brother Richard from a string of investments, some of which were made during the ‘wild capitalism’ of the post-Soviet economy.

Tonight one leading MP called for an investigation by Parliament’s intelligence and security committee into the Legatum Institute and its influence on the Government.

But an Institute spokesman strongly defended the charity’s influence in the Brexit letter, and denied that Mr Chandler had played any role.

It comes amid a separate political row over claims that the Kremlin secretly interfered in both Brexit and the election of Donald Trump. This newspaper has traced thousands of pro-Brexit social media posts to a ‘troll factory’ based in St Petersburg.

Mr Singham and Mr Gove were both at a behind-closed-doors Commons seminar on Brexit on Friday, which was also attended by No 10 and officials from the US Embassy. All guests were sworn to secrecy.

The Mail on Sunday photographed Mr Singham as he slipped out of the meeting on Friday afternoon.

Asked about his links with the Legatum Institute, Mr Gove told this newspaper he had met one of the Chandler brothers on one occasion. But he declined to comment on Friday’s meeting with Mr Singham, or Mr Singham’s role in the letter, saying: ‘The blessed sponge of amnesia wipes the memory slate clean.’

Johnson and Gove’s Legatum-backed letter, revealed by The Mail on Sunday a fortnight ago, made three key demands to Mrs May: to force Chancellor Philip Hammond to do more to plan for a ‘hard Brexit’; to use our withdrawal from the EU to scrap swathes of rules and regulations; and to appoint a new ‘Brexit Tsar’ to head up a task force within Whitehall.

All three demands seem to have been met. Mr Hammond used the Budget to announce an extra £3 billion to prepare for a ‘no deal’ on Brexit talks. Mr Gove has reportedly boasted that he has won Mrs May’s backing to use our EU withdrawal to break free of all Brussels rules.

And our investigation suggests that Mr Singham is effectively becoming that Tsar: over the past year, he has held at least seven secret meetings with Ministers and officials at DexEU – the Department for Exiting the EU – including a summer summit at Chevening, the Kent home shared by Johnson, Brexit Secretary David Davis and International Trade Secretary Liam Fox. Mr Singham, who has dual UK and US citizenship, has worked on trade deals involving Russia in the past.

He previously spent 18 years working for US law firm Squire Sanders, which was subsequently dragged into the row over Donald Trump’s links to Russia. The company formed an alliance with one of the President’s former lawyers, Michael Cohen, who had been embroiled in controversy for approaching Putin’s spokesman for help on a property deal.

The tycoon bought La Fleur Du Cap, the old mansion on the French Riviera formerly owned by David Niven

Asked if Mr Singham had helped write the letter to Mrs May, Mr Gove declined to answer four times before claiming he had forgotten. The Environment Secretary confirmed he had met Mr Singham, an Oxford University contemporary.

He also said he had met Monaco-based Christopher Chandler, who fiercely guards his privacy, at an event backed by the Legatum Institute and hosted by former Tory Cabinet Minister Lord Cranborne.

The Chandlers extended their flourishing business empire into Russia in the 1990s, when state businesses were being privatised, and lucky entrepreneurs were able to make a killing. Through their company, Sovereign Global, they built a substantial holding in Gazprom, the government-controlled energy giant.

Shortly after Putin became Russian President for the first time in 2000, the Chandlers, angered by the corruption they had witnessed in Gazprom, were credited with helping to trigger a boardroom coup which subsequently led to Alexey Miller being installed as head of the company. The Chandlers say they helped to bring ‘transparency and accountability’ to the company. Miller was a close ally and confidant of Putin’s from their time working together in St Petersburg.

Putin used the vast profits from Gazprom, the world’s largest energy company, to consolidate his grip on power. In 2005 another Putin ally, Dmitry Medvedev, the current Prime Minister, became chairman of Gazprom.

The brothers split their fortunes in 2006, with Christopher using his share to help form the Legatum Group, which operates from Legatum Plaza in Dubai. The Legatum Group then spawned the Legatum Institute, which the group says is a completely independent charity with its own trustees.

The Legatum Institute has played a key role in pushing Mrs May’s Government closer to a ‘hard Brexit’ deal.

Who's behind - and what drives - Legatum? Q What is the Legatum Institute? A It is a mysterious Mayfair-based think-tank which has become a hot house for Eurosceptic ‘hard’ Brexit ideas. Q Who funds it? A The vast bulk – nearly 90 per cent – of its £4 million-a-year income comes from the Legatum Foundation; this was spun out of the Legatum Group created by tycoon Christopher Chandler a decade ago after splitting the fortune he made in emerging markets with brother Richard. Q What is the Institute’s purpose? A ‘Legatum’ means legacy: it says it is focused on ‘tackling the major challenges of our generation’. Brexit is certainly that. Q How did it influence the Boris-Gove letter? A Shanker Singham, Legatum’s director of economic policy, secretly helped to draw up the ‘hard’ Brexit trade policies advocated by Gove and Johnson – including preparing for a no-deal Brexit. Q What is its input on Brexit? A Legatum’s experts appear to have untrammelled access to Ministers: and in the case of Crawford Falconer have supplied the Government with its senior trade negotiator. Q Has the institute done anything wrong? A Civil servants resent the fact that Mr Gove and Mr Johnson appear to be using it as a ‘parallel Whitehall’. But it has not broken any rules. Advertisement

It referred questions to the Legatum Group, which last night confirmed that Mr Singham is advising the Government because of his ‘unparalleled expertise in economics and trade as a public service.’

The spokesman said Mr Chandler was ‘not aware’ of the Johnson/Gove letter. He added that Mr Chandler had made his money in many endeavours, not just Russia, was ‘not involved in running the Legatum Institute’ and had no ‘role in appointing Mr Singham’.

According to the institute’s accounts, it received more than £4.4 million in funding last year – of which £3.9 million came from the Legatum Foundation, the ‘development wing’ of the Legatum Group.

The Johnson/Gove letter is not the only thing linking the organisation to the Government:

lIt paid Brexit Secretary David Davis £5,000 to make a speech at its London office and flew him to Los Angeles for another function;

lLegatum Institute trade expert Crawford Falconer was appointed Liam Fox’s chief trade negotiator two months ago;

lAnd Legatum Institute ‘senior fellow’ Matthew Elliott was chief executive of Gove and Johnson’s ‘Vote Leave’ referendum campaign.

Mr Elliott was previously caught up in a Russian controversy in 2012, when he was targeted by a man the Home Office now believes was a Russian spy.

Russian diplomat Sergey Nalobin cultivated links with Elliott and helped to found Conservative Friends of Russia, which was later revealed to have links to Russian intelligence.

But in August 2015, Nalobin had his permission to stay in Britain suddenly revoked after the inquiry into the death of Alexander Litvinenko by polonium poisoning in London concluded that he was probably murdered on the personal orders of Putin.

The Chancellor’s £3 billion Budget boost, and claims that Mrs May now supports Mr Gove’s demand to ditch EU standards will fuel claims the Government is following the Legatum Institute’s Brexit blueprint.

Furthermore, the charity’s involvement in the secret Johnson-Gove letter and Friday’s behind-closed-doors Commons summit will lead to more questions about the alleged cloak-and-dagger aspects of the organisation’s influence.

One senior Government source claimed the institute had ‘staged a soft coup via Johnson and Gove’ and that civil servants who have to obey strict anti-corruption rules had effectively been bypassed.

Mr Johnson is to visit Russia in December for talks with Vladimir Putin in his role as Foreign Secretary. Brexit is expected to be on the agenda.

Labour MP Liam Byrne, a former Chief Secretary to the Treasury, said: ‘In the light of The Mail on Sunday’s revelations of the close links between the Legatum Institute and the Johnson-Gove hard Brexit putsch, it is now critical that this think-tank’s relationship with the Government is thoroughly investigated. I urge Parliament’s intelligence and security committee to launch a wide inquiry into Russian interference and settle the serious and lingering questions’.