Boris Johnson today faced an extraordinary bid by a senior Tory to oust him before he even becomes PM.

Sir Alan Duncan - a long-time foe of Mr Johnson who was once his deputy at the Foreign Office - announced his resignation on the eve of the new Conservative leader being installed.

And he immediately tabled an emergency motion to force a Commons vote on whether Mr Johnson had the right to form a government.

The explosive tactic was seemingly designed to expose Mr Johnson's wafer-thin majority and stop him ever taking office, despite Sir Alan saying he would have supported the new Tory leader. However, it was blocked by the Speaker as breaking Parliamentary procedure.

It underlines the mammoth task facing the new premier to hold the Tories together amid furious infighting over Brexit.

One Tory MP told MailOnline the idea pushed by Sir Alan was 'bonkers' and showed that he was 'dripping in arrogance'.

Sir Alan's departure this morning immediately sparked claims that a slew of ministers will follow him out of the door as Theresa May's premiership enters its final 48 hours.

Chancellor Philip Hammond and Justice Secretary David Gauke have already made clear they will quit on Wednesday before Mrs May formally stands down. Health minister Stephen Hammond and defence minister Tobias Ellwood are also believed to be among those considering their positions.

Meanwhile, former PMs Tony Blair, Gordon Brown and John Major have all heaped pressure on Mr Johnson by warning him against No Deal, saying he must not represent an 'ultra-Brexit faction'.

Boris Johnson will have a wafer-thin Commons majority of just four when he becomes PM, which could fall to two if the Tories lose a by-election next month. His Brexit plan faced a double blow last night before he even enters No 10

Sir Alan Duncan (pictured in Westminster today) - a long-time foe of Mr Johnson - announced he had resigned just a day before the new Tory leader is due to be installed

In his resignation letter today, Sir Alan said he regretted his attempts to free Nazanin Zaghari-Ratcliffe were 'abruptly ended'

Tory MP Ben Bradley, a supporter of Mr Johnson, hit back by joking that he was 'crying a river' and playing a 'tiny violin'

The last ConHome poll of activists suggests that Mr Johnson has trounced Mr Hunt in the leadership contest

Mr Johnson is almost certain to defeat Jeremy Hunt for the Conservative leadership tomorrow, and is then expected to take over from Mrs May in Downing Street on Wednesday after her final PMQs. The final ConHome poll of party activists suggests he could be on track to trounce his rival by 73 per cent to 27 per cent.

Some allies are urging him to sack Mr Hunt if he wins by a big margin, saying the Foreign Secretary should 'take responsibility' for blunders in the Iran tanker crisis.

Sir Alan Duncan's beef with Boris Johnson goes back years Sir Alan Duncan's beef with Boris Johnson goes back years. The Tory MP previously described Mr Johnson as a 'circus act' when it emerged that his former boss at the Foreign Office had described the French as 'turds' over their approach too Brexit. During the 2016 Conservative leadership contest Sir Alan jibed about Mr Johnson's tangled love life by branding him 'Silvio Borisconi'. Earlier this month, Sir Alan accused the Tory favourite of throwing Sir Kim Darroch, the UK's former ambassador to Washington, 'under the bus' by failing to stand up for him when Donald Trump raged about leaked diplomatic cables. 'His disregard for Sir Kim Darroch and his refusal to back him was pretty contemptible and not in the interests of the country he is hoping to lead,' Sir Alan said at the time. Advertisement

However, other allies played down speculation Mr Hunt could be axed, telling MailOnline they will 'kiss and make up' after bitter clashes during the contest.

The former London mayor demanded a more positive attitude this morning, comparing Brexit to the moon landings.

He said if technology 50 years ago could achieve space travel then it could solve the Irish border issue.

However, the comparison was lampooned by Labour former PM Tony Blair, who pointed out that they were 'technically different' and warned that the EU will not give ground on the backstop.

In his resignation letter earlier, Sir Alan sniped that he was frustrated at working under the 'dark cloud of Brexit' - and also took aim at Mr Johnson's handling of the case of British mother Nazanin Zaghari-Ratcliffe, who has been jailed in Iran.

But supporters of Mr Johnson hit back by joking that they were 'crying a river' and playing a 'tiny violin'.

In a round of interviews this afternoon, Sir Alan said Mr Johnson flew by the 'seat of his pants'.

'The fundamental principle of our democracy is that the PM is the person who can command a majority in the House of Commons,' he said.

'That will not be tested and that is in doubt.

He added: 'The Speaker has denied me and the House that opportunity.'

However, a Tory Brexiteer said: 'We are going through a process of the party membership electing the next leader of the Conservative Party who will then form the next government and it seems to me that Sir Alan not only cannot accept the result of the referendum but he also cannot accept the result of a contest which hasn't even finished yet.

Sir Alan immediately tabled an emergency motion to force a Commons vote on whether Mr Johnson had the right to form a government

'It is an awful denial of democracy taking its course. He is absolutely dripping arrogance. It is called democracy.

How would Alan Duncan's emergency motion have worked? Sir Alan Duncan said he quit so he could table an emergency motion to test the new PM's majority. He asked Speaker John Bercow to accept a 'Section 24' debate stating the House had 'considered the merits of the newly chosen Leader of the Conservative Party, and supports his wish to form a government'. The move would have hit Mr Johnson before he is due to become PM on Wednesday. The government only has a wafer-thin effective majority of two. However, the Speaker ruled that the motion breached Parliamentary procedure and refused to allow it. The rules state that S24 motions must be on 'neutral terms' - merely saying that that House has considered an issue. Formally confidence votes can also only be tabled by the official Opposition. Advertisement

'It is just bonkers. He should consider in his retirement living in North Korea.'

Among half a dozen senior ministers are expected to resign on Wednesday, when Theresa May leaves office, rather than being sacked.

But Sir Alan, who was Mr Johnson's deputy at the Foreign Office and recently lambasted him for failing to defend US ambassador Sir Kim Darroch, decided to take matters into his own hands today.

He wrote: 'The UK does so much good in the world. It is tragic that just when we could have been the dominant intellectual and political force throughout Europe, and beyond, we have had to spend every day working beneath the dark cloud of Brexit.

'On a heartfelt personal note, I have known you and Philip for over 40 years, throughout which you have both displayed faultless dignity and an unstinting sense of duty.

'I am only sorry that your three years as prime minister have been brought to an end. You deserved better.'

There are claims more could follow Sir Alan's example by tonight.

In addition, six more MPs are rumoured to be planning to defect to the Liberal Democrats if he becomes the party's new leader.

Sir Alan previously described Mr Johnson as a 'circus act' when it emerged that Mr Johnson had described the French as 'turds' over their approach too Brexit.

Pound tumbles amid Brexit warning on UK economy The pound tumbled by nearly half a per cent today as a leading think-tank warned on Brexit and cast doubt on the health of the UK economy. The currency dropped 0.4 per cent against the dollar to $1.245, and the same against the euro, as Boris Johnson closed in on victory in the Conservative leadership contest. Today's slide in the pound was not helped by a gloomy report from the National Institute of Economic and Social Research, which revealed a one-in-four chance that the UK economy is already experiencing a technical recession – before the country has officially left the bloc. Advertisement

During the 2016 Conservative leadership contest Sir Alan jibed about Mr Johnson's tangled love life by branding him 'Silvio Borisconi'.

Earlier this month, Sir Alan accused the Tory favourite of throwing Sir Kim Darroch, the UK's former ambassador to Washington, 'under the bus' by failing to stand up for him when Donald Trump raged about leaked diplomatic cables.

'His disregard for Sir Kim Darroch and his refusal to back him was pretty contemptible and not in the interests of the country he is hoping to lead,' Sir Alan said at the time.

Mr Johnson is not just facing trouble from within his own party, as the EU ramps up its rhetoric ahead of what promises to be bitter negotiations in the run-up to October 31.

Yesterday the Irish government took a hardline stance against his demand for a better Brexit deal.

Ireland's deputy prime minister Simon Coveney insisted the EU would not renegotiate the withdrawal agreement and rejected outright the idea of a time limit on the Northern Ireland backstop.

But in a sign of difficulties he faces once in Downing Street, senior ministers opposing No Deal including Philip Hammond and David Gauke (above) announced they would quit the Government if he becomes Prime Minister

Chancellor Phillip Hammond is also among half a dozen ministers expected to resign on Wednesday, when Theresa May leaves office, rather than being sacked

Margot James, who resigned as a culture minister last week to support efforts to stop Parliament being suspended, has denied she is currently thinking about defecting to the Liberal Democrats

Last night Mr Johnson was finalising the list of senior Downing Street staff to join him in No 10 and work in his Cabinet.

Who else could quit as the Boris Johnson era kicks off? Chancellor Philip Hammond Justice Secretary David Gauke International Development Secretary Rory Stewart Health minister Stephen Hammond Energy minister Claire Perry Possible defectors to Lib Dems: Phillip Lee, Sam Gyimah, Margot James Advertisement

Expectations of his victory were raised by a ConservativeHome poll showing up to 73 per cent of Tory members back him for leader, in what would be a landslide over Jeremy Hunt.

The result will be announced shortly after 11am tomorrow. Mrs May will conduct her final Prime Minister's Questions on Wednesday before she goes to Buckingham Palace to resign. Mr Johnson is then expected to make his first speech as PM outside No 10 at around 5pm and begin making Cabinet appointments later in the evening.

He has promised to leave the EU 'do or die' on October 31, and last week toughened his Brexit stance by insisting he would not accept minor changes to the Irish backstop.

But up to half a dozen ministers in the so-called 'Gaukeward Squad' – named after Justice Secretary Mr Gauke – strongly opposed to No Deal are expected to walk out on the day and begin organising against him from the backbenches.

Former PMs warn Boris over No Deal Brexit Three former prime ministers have told Boris Johnson he must choose between leading the UK and being a 'spokesman for an ultra-Brexit faction' as they warned him not to take Britain out of the EU without a deal. Tony Blair, Gordon Brown and Sir John Major joined forces today to launch an anti-No Deal pincer movement against the man expected to be installed as the next PM on Wednesday. Sir John warned his fellow Conservative that should he pursue a No Deal Brexit 'he cannot complain if he faces uncompromising opposition from those who believe they have had their views ignored'. Mr Blair ridiculed the former mayor of London's Brexit plan, insisted the EU will dismiss any attempt to ditch the Irish border backstop and told him to stop letting Nigel Farage dictate policy. Meanwhile, Mr Brown issued a grave No Deal warning as he said leaving the bloc without an agreement would be 'deeply damaging' and compared it to the Charge of the Light Brigade. All three former premiers are stridently against No Deal but while their politics on Brexit are widely known, the timing of their intervention, all coming on the same day, will put pressure on Mr Johnson to reconsider his stance. Advertisement

Mr Johnson will have a wafer-thin Commons majority of just four when he becomes PM, which could fall to two if the Tories lose a by-election next month.

Yesterday morning Mr Hammond announced he would quit before he is pushed and repeated his determination to stop a 'catastrophic' No Deal Brexit. Asked on the BBC's Andrew Marr Show if he thought he would be sacked, he replied: 'No, I'm sure I'm not going to be sacked because I'm going to resign before we get to that point.

'Assuming that Boris Johnson becomes the next prime minister, I understand that his conditions for serving in his Government would include accepting a No Deal exit on October 31, and it's not something I could ever sign up to.

'It's very important that the Prime Minister is able to have a Chancellor who is closely aligned with him in terms of policy, and I therefore intend to resign to Theresa May before she goes to the Palace to tender her own resignation on Wednesday.'

Mr Gauke told The Sunday Times he would also quit, adding: 'If the test of loyalty to stay in the Cabinet is a commitment to support No Deal on October 31 – which, to be fair to him, Boris has consistently said – then that's not something I'm prepared to sign up to.

'I recognise that this spell in government is coming to an end. Given that I've been in the Cabinet since Theresa May came to power, I think the appropriate thing is for me to resign to her.'

Mr Hammond said Parliament 'does have a way of preventing a No Deal exit on October 31 without parliamentary consent', adding: 'I intend to work with others to ensure Parliament uses its power to make sure that the new Government can't do that.'

Will Tory MPs join Lib Dems? Six Tory MPs may defect to the Liberal Democrats if Boris Johnson is anointed Conservative leader tomorrow, it was claimed yesterday. The rebel group are due to hold talks with the pro-Remain party this week and could discuss voting against Mr Johnson in a vote of no confidence, The Sunday Times reported. It is said they could even consider joining the Lib Dems – depriving Mr Johnson of a majority even with the backing of the DUP. Sir Ed Davey, who served as Lib Dem energy minister in the coalition cabinet with leading Tory remainers, is understood to have been approached by Conservatives desperate to stop Mr Johnson. Advertisement

Several other ministers could also quit on the day, sources suggested, including International Development Secretary Rory Stewart, health minister Stephen Hammond and energy minister Claire Perry.

However, Business Secretary Greg Clark has told friends he will not quit and could remain in the Government.

Irish deputy Mr Coveney rebuffed suggestions the EU would compromise with Mr Johnson on the existing Brexit deal 'just because there's a change in personality as British Prime Minister', saying: 'We're simply not going to move away from that Withdrawal Agreement.

'The facts don't change around Brexit. The complexity doesn't change. The vulnerabilities on the island of Ireland don't change.

'The EU I think has made it very clear that we want to engage with the new British Prime Minister, we want to avoid a No Deal Brexit.'

He described Mr Johnson's approach was 'give me what I want or I'm going to burn the house down for everybody'.

Sir Alan Duncan's resignation letter from the Foreign Office Dear Prime Minister It is customary for all Ministers to stand down on the departure of a Prime Minister, and I am writing to resign now in anticipation of the change on Wednesday. I am doing so a couple of days early in order to be free to express my views in advance of you relinquishing office. Despite playing an active role in your leadership campaign I had not sought further ministerial office, but remain deeply grateful to you for recalling me to the colours three years ago. I have served with two very different Foreign Secretaries, holding responsibility for 77 countries across all of the Americas, Europe, Russia, Turkey and Central Asia. I was pleased to build a strong relationship with Turkey in the immediate aftermath of the coup attempt. I have re-set our relationship with Argentina and established additional flights to the Falklands; have put the UK in the forefront of international co-operation on Venezuela; have negotiated the eviction of Julian Assange from the Ecuador embassy, and then re-launched our relations with Ecuador itself. I have played my part in handling our vexed relationship with Russia, and in helping ensure last year's Western Balkans summit in London was such a success. Perhaps most fulfilling has been the steady nurturing of UK engagement in Central Asia, where a personal focus on Uzbekistan's reform path helped lead to the release of a raft of political prisoners and the admission to the country of the BBC, the Economist and Reuters. Rather less successfully, it was disappointing that our efforts to secure an agreement on the future of Cyprus failed, and I remain deeply upset that some fruitful discussions I had initiated about the possible release of Nazanin Zaghari-Ratcliffe were brought to such an abrupt halt. The Foreign Office deserves far more recognition (and resources!) for the excellent work it does for our country, and I salute all who work in it with such integrity. The UK does so much good in the world. It is tragic that just when we could have been the dominant intellectual and political force throughout Europe, and beyond, we have had to spend every day working beneath the dark cloud of Brexit. On a heartfelt person note, I have known you and Philip for over forty years, throughout which you have both displayed faultless dignity and an unstinting sense of duty. I am only sorry that your three years as Prime Minister have been brought to an end. You deserved better, but please take lasting comfort from the knowledge that your self-esteem (sic) can, and will forever, far exceed that of your critics. Yours Ever Alan Advertisement