Theresa May is effectively being held to ransom over Brexit by Boris Johnson and Michael Gove, a bombshell leaked letter reveals.

The Cabinet heavyweights made a series of veiled threats in a secret missive to the Prime Minister – which contained blunt instructions on how she should deliver the ‘hard Brexit’ they demand.

The incredible letter also contains the sinister-sounding instruction that Mrs May should make rebel Cabinet Ministers toe their line by ‘clarifying their minds’.

Theresa May is effectively being held to ransom over Brexit by Boris Johnson and Michael Gove, a bombshell leaked letter reveals

It lays bare Cabinet tensions and will fuel claims that the Brexit stance of Mrs May – who supported the Remain campaign during the EU referendum – is being dictated by Mr Gove and Mr Johnson.

One senior Government figure, who has seen the letter, said it showed that Foreign Secretary Johnson and Environment Secretary Gove had conducted a ‘soft coup’ and that Mrs May was ‘their Downing Street hostage’.

It comes amid continuing speculation of a leadership challenge to Mrs May, who has struggled to impose her authority since the botched General Election.

In the missive, the Brexit cheerleaders:

Instruct the embattled Prime Minister in blunt terms to ‘underline her resolve’ to achieve a total break with Brussels;

Accuse Chancellor Philip Hammond, who wants a soft Brexit, of not showing ‘sufficient energy’ and letting the EU hold Britain ‘over a barrel’ by refusing to plan for the possibility Britain walks away from talks with no deal on trade relations;

Under the cosh: The Cabinet heavyweights made a series of veiled threats in a secret missive to Theresa May (pictured) – which contained blunt instructions on how she should deliver the ‘hard Brexit’ they demand

BARE-FACED GALL OF THE BREXIT DUO'S DEMANDS... Post-Brexit transition must end on June 30, 2021 Stop Hammond letting EU ‘hold you over barrel’ ‘Ossified’ mandarins must not wreck Brexit Gag Ministers who’ve ‘not internalised’ Brexit Meet us ‘when you consider it wise’ Advertisement

Lecture the Prime Minister on how to run ‘your government’ – and say it is vital for her to display more ‘confidence’;

Tell her to ‘articulate the following’ – and then set out their own hard Brexit manifesto – including naming June 30, 2021, as the fixed end of Britain’s transition period after we leave the EU in March 2019.

Government insiders say the letter, the contents of which have been made known to The Mail on Sunday, was sent last month. It will send shockwaves around the Government.

A well-placed source said it suggested Mr Gove and Mr Johnson were running what was tantamount to a ‘hard Brexit cell’ inside the Cabinet.

The cloak-and-dagger nature of the ultimatum is illustrated by the James Bond-style instruction that the letter is ‘for your and Gavin’s eyes only’ – a reference to Mrs May’s No 10 chief of staff, the former Conservative MP Gavin Barwell.

It is understood the letter was delivered to him by hand by Mr Johnson. But the pair could face a backlash for appearing to order her not to show it to other Cabinet Ministers or Whitehall mandarins.

...IN PATRONISING LETTER HANDED TO CHIEF OF STAFF EU Exit – Next Steps. ‘For your and Gavin’s eyes only.’ Your approach is governed by sensible pragmatism. That does not in any way dilute our ambition to be a fully independent self-governing country by the time of the next election. If we are to counter those who wish to frustrate that end, there are ways of underlining your resolve. We are profoundly worried that in some parts of Government the current preparations are not proceeding with anything like sufficient energy. We have heard it argued by some that we cannot start preparations on the basis of ‘No Deal’ because that would undermine our obligation of ‘sincere co-operation’ with the EU. If taken seriously, that would leave us over a barrel in 2021. We all want you to push your agenda forward with confidence and have your Government articulate the following... Yours, Boris and Michael Advertisement

The letter includes the Orwellian- threat to ‘clarify the minds’ of rebel Ministers and make them ‘internalise the logic’ of the Johnson-Gove approach to the EU. In another jibe at Ministers such as Mr Hammond who opposed leaving the EU, it says Mrs May must ensure all Cabinet members take the same tough line on Brexit – ‘whatever their original positions during the referendum’.

They should not even be allowed to express doubts about the final outcome of Brexit behind closed doors and must echo Mrs May’s stance word for word ‘publicly and privately,’ they argue. And the ‘Whitehall machine’ and its ‘ossified ways of working’ cannot be ‘left to its own devices’ to deliver Brexit. New high-powered staff are needed to ‘apply grit to the oyster’.

The tone of the letter is as shocking as its contents. It ranges from quietly menacing to ingratiating flattery, such as praising how Mrs May’s ‘excellent speech in Florence landed well’.

The cloak-and-dagger nature of the ultimatum is illustrated by the James Bond-style instruction that the letter is ‘for your and Gavin’s eyes only’ – a reference to Mrs May’s No 10 chief of staff, the former Conservative MP Gavin Barwell (pictured)

Government sources believe the letter may have been drawn up with help from the pro-Brexit European Reform Group of Tory MPs and the Legatum Institute think-tank.

The letter says Mrs May’s ‘sensible pragmatism’ is no excuse for watering down Brexit – and that to ‘counter those who wish to frustrate that end, there are ways of underlining your resolve’.

Mr Johnson and Mr Gove do not name Mr Hammond but refer to his comment that Britain had to engage in ‘sincere co-operation’ with the EU, saying such a stance would ‘leave us over a barrel’.

The pair also warn Mrs May to rein in Mr Hammond over claims he refuses to spend public money planning for a ‘no deal’ outcome.

Clearly, both issues still rankle with Mr Johnson and Mr Gove, who write: ‘We are profoundly worried that in some parts of Government the current preparations are not proceeding with anything like sufficient energy… We all want you to push your agenda forward with confidence and have your Government articulate the following’ – and set out their own Brexit manifesto.

The letter ends with a conspiratorial offer by the pair to meet Mrs May to discuss her response ‘as and when you consider wise’.

A No 10 spokesman said: ‘We do not comment on leaks.’ Asked why Mr Johnson and Mr Gove had bypassed Whitehall officials, the spokesman added: ‘It is common practice under governments of all colours for Cabinet Ministers to offer advice and views to the PM.’

Mr Johnson and Mr Gove declined to comment.

What DO they think they're doing?

Analysis by political correspondent Glen Owen

The ‘Brexit ultimatum’ from two of Mrs May’s most ambitious and calculating Ministers is the starkest illustration of her struggle to maintain discipline in a Cabinet riven with warring factions.

Mr Johnson and Mr Gove made their move in the wake of her calamitous speech to the Tory Party Conference.

Despite their protestations of loyalty, they smelt weakness – and have seized the opportunity to strike against the Remain camp in Cabinet, headed by Philip Hammond. The Brexiteers are infuriated by what they see as the Chancellor’s pursuit of a ‘Brexit lite’ in which the UK shadows the single market for a long transition period – which is why Johnson and Gove have demanded a set date for the end of the transition. They have also been angered by Hammond’s reluctance to spend money preparing for the chance of a ‘no deal’ Brexit, which they say makes failure in the Brussels negotiations more likely because it ‘weakens our hand’.

There are already signs that the enfeebled PM has been forced to act on their demands: her pledge on Friday to enshrine in law the start of Brexit is in the spirit of their call for a strict timeline for the transition.

And last week’s announcement that Mr Gove was joining a ‘war cabinet’ of six predominantly Leave-backing Ministers plotting Britain’s negotiation strategy fits with their call for No 10 to take greater control of the Brexit process.

With the number of Tory MPs who want Mrs May to stand down now close to 40, her grip on power is too fragile for her to resist.

How Boris and Gove buried hatchet

by Glen Owen

THE joint letter shows how the on-off Brexit bromance between Michael Gove and Boris Johnson has been rekindled by shared ambition.

Mr Gove, the man who spectacularly torpedoed Mr Johnson’s leadership hopes last year, has formed a deadly Cabinet axis with the Foreign Secretary to strongarm Theresa May into enacting their vision of Brexit.

The pair, contemporaries at Oxford, have been friends, through journalism and politics, for decades. But it was when they met at Mr Johnson’s home in February 2016 for a secret dinner – revealed by The Mail on Sunday – that they agreed the explosive political pact which led to Britain severing its ties with the EU.

The combination of Mr Gove’s brains and Mr Johnson’s campaigning flair propelled the Leave campaign to victory in the referendum later that year. They looked set to take the double act into Downing Street, with Mr Gove backing Mr Johnson for leader following Mr Cameron’s resignation.

But hours before the deadline closed for candidates, Mr Gove withdrew his support and announced he was running in his own right, killing Mr Johnson’s hopes in the process. The move backfired, and appeared to have destroyed their friendship for good. Now, despite the mutual wariness of their respective entourages, they have buried the hatchet for fear of being accused of reneging on promises they made during the campaign.

The first public sign of their rapprochement came after Mr Johnson published his 4,000-word ‘Brexit manifesto’ in September, with Mr Gove making supportive remarks.

They have calculated that they are stronger together than they are apart.

So was Dubai-backed think-tank behind letter?

Government insiders believe the Johnson-Gove letter was written with advice from the Tory European Reform Group, which in turn has close links with the Legatum Institute.

The think-tank, seen as Right of centre, is run by Baroness Philippa Stroud, ex-aide to Brexit cheerleader and former Cabinet Minister Iain Duncan Smith.

Earlier this year, Matthew Elliott, chief executive of the official Vote Leave campaign, joined as a senior fellow.

The wealthy Mayfair-based institute is funded by a Dubai-based investment bank.

Some insiders believe the ERG is using the institute’s resources to provide a ‘shadow civil service’ on Brexit – to counter claims that most senior Whitehall mandarins are ‘unenthusiastic’ about Brexit.

A spokesman for the institute said: ‘The Legatum is politically neutral, and has never provided funding to the ERG.’

One ERG member denied that the group advised Gove and Johnson.