TWELVE ex-ministers have written to all Tory MPs calling on them to vote down Theresa May’s deal tomorrow in a 24-hour battle to save Brexit.

The dozen, including Boris Johnson, demand in their Plan B letter that the PM issue the EU with a final ultimatum for a better deal when hers is voted down on Tuesday - and then leave without one.

The senior figures call on the PM to ask EU leaders to free Britain from a never-ending Irish backstop.

If they refuse, Mrs May must “have the confidence to leave on WTO terms” on March 29 as the only way to stay true to her election manifesto last year.

Their explosive intervention comes as the PM also today declares there are just 24 hours left to save Brexit ahead of the landmark Commons showdown over it tomorrow night.

A reversal of the referendum decision rather than no deal is now the most likely outcome if her divorce agreement with Brussels falls, Mrs May will insist.

As British politics enters a momentous week, academics predicted her almost certain defeat will trigger the biggest political crisis since World War Two.

Ahead of it yesterday as the tension ratcheted up;

A “cloakroom plot” by backbench MPs to seize control of Parliamentary business and sideline the Government over Brexit was allegedly uncovered,
A cross party group of MPs - including a former Tory Cabinet minister – today reveal they have already drawn up a new bill to enforce a second EU referendum,
Jeremy Corbyn infuriated Labour members by revealing he personally opposes a second referendum,
Military planners have been seconded to a series of Government ministries in case the Army needs to be called in to manage a No Deal Brexit,

The ultimatum letter is also signed by David Davis, Dominic Raab, ex-Tory leader Iain Duncan Smith, Priti Patel, Esther McVey, Owen Paterson, John Whittingdale and four other senior former ministers.

It only deepens the PM’s appalling dilemma and will now see a serious split in the Tory party, whatever she does.

If, as all expect, her deal is heavily torpedoed by the Commons, Mrs May must either go for no deal and alienate Tory moderates, or soften Brexit with Labour's help and lose the support of the Leavers.

In a further blow for Mrs May, The Sun can also reveal the big beasts’ demand is backed by the DUP.

The Ulster unionist party chief will share a platform with Mr Davis and Mr Raab tomorrow to spell out their demands to the EU in greater detail.

In the letter, leaked to The Sun, the Brexiteers write: “We urge colleagues to look beyond the day-to-day news cycle, to consider the long-run future of our country, and to vote against this agreement.

“By voting down this flawed Withdrawal Agreement we can encourage the EU to renegotiate and take out backstop or all out a unilateral right to leave it.

“The EU will need to remove the most problematic parts, notably the backstop, or provide a method by which the UK has the unilateral right to leave it.

“In the event that the EU is unwilling to commit to this, then we can and must fulfil the democratic wishes of the people of the UK.

“That is why, if it is the only way forward, we must have the confidence to be ready to leave on WTO terms.”

The Brexiteers admit in the letter that leaving without any deal would cause economic pain – which they dub “some short-term inconvenience and disruption”.

But they insist “the much greater risks” are to agree to be locked into “a very bad deal” that enforces a customs union on the UK for as long as the backstop lasts.

As Westminster braced itself for a historic week, the almost sure defeat of Mrs May’s deal will spark the biggest political crisis since World War Two, academics predicted.

Renowned historian Lord Hennessy said British politics will enter “a multiple crisis” over what to do about Brexit, the country’s unwritten constitution, Westminster’s two party system and voters’ faith in politics in general.

Peter Hennessy added: “All of that adds up to a crisis with a capital C”.

The PM will deliver a speech today in a Labour-voting town that also strongly backed Brexit, in a bid to ram home her point to wavering Labour MPs.

Sounding the alarm about Remain MPs plotting to keep the UK in the EU with Speaker John Bercow’s help, the PM will tell factory workers in the Midlands:
“As we have seen over the last few weeks, there are some in Westminster who would wish to delay or even stop Brexit and who will use every device available to them to do so.”

She will issue her strongest attack yet on MPs wanting to reverse Brexit, saying: “I ask MPs to consider the consequences of their actions on the faith of the British people in our democracy.

“What if we found ourselves in a situation where Parliament tried to take the UK out of the EU in opposition to a remain vote?

“People’s faith in the democratic process and their politicians would suffer catastrophic harm.”

Mrs May won a small boost last night as four wavering Tory MPs declared they would voting for the PM’s deal – Sir Edward Leigh, Sir Geoffrey Clifton-Brown, Caroline Johnson and Andrew Murrison.

But an honours controversy surrounded veteran Eurosceptic Sir Edward’s decision, as it came just two weeks after he was made a Privy Counsellor.

Another Leave-backing Labour MP, John Mann, also pledged to support it but admitted that very few of his colleagues planned to do the same, and he’d be surprised “surprised if it’s anything like enough to get this deal through”.

Projections still put Mrs May on course for a catastrophic defeat by around 200 votes – the biggest for a Goverment on record.

A raft of senior Tories began to public with alternative courses of action to end the crisis.

The most controversial came from pro-EU rebel leader and former Attorney General Dominic Grieve.

Mr Grieve – who was also accused of plotting with Speaker John Bercow to reverse Brexit - revealed he is among a cross party group of MPs and peers to have now drawn up a new bill that would bring in a second EU referendum.

Working alongside Lib Dem leader Sir Vince Cable, the former Cabinet minister dubbed it “an escape hatch” for Mrs May to end the deadlock.

Sir Vince also claimed a Commons bid to soften or reverse Brexit by handing power to MPs was indeed underway, and he was even “talking to Cabinet ministers” about joining it, adding: “It’s not a conspiracy, but it’s clearly happening”.

But he and other plotters were rounded on by Transport Secretary Chris Grayling, who warned them it would be a “huge mistake” to kneecap the Government by changing the Commons rules to allow any MP to pass laws.

Former Tory PM John Major stepped up his call for Mrs May to pause Brexit by revoking the Article 50 departure process for now.

A “new process” of national consultation is now required, the ex-party leader argued, to avoid a "damaging" no-deal Brexit.

But Brexit Secretary Steve Barclay signalled what was likely to be No10’s Plan B by suggesting Mrs May will call a second vote on her deal after some tweaks.

He told BBC1’s Andrew Marr Show "strongly suspects" the Commons will end up voting for “something along the lines” of the current deal.

It was also reported yesterday that the EU assurances on the deal – which could come today - will fall significantly short of Tory MPs’ demands.

Letters from Brussels bosses will pledge their “firm determination” to end the backstop by January 2021, but without any commitment to do it.

There is also expected to be a promise to expedite trade talks so a deal can be in place as quickly as possible, limiting the length of any backstop or its need at all.

But Tory hardline Brexiteer Mark Francois dubbed them “meaningless”, adding: “A love letter doesn’t change the terms of the treaty”.