Liam Fox says UK 'a sitting duck' if it stays in EU

Senior Tories campaigning to keep Britain in the EU are hopeful that the referendum is swinging their way. They believe that opinion polls in recent days, which have given the Remain side a noticeable lead, show that a series of warnings about the impact of a British exit from Barack Obama, the IMF and the Bank of England are hitting home.

But the Leave side insists there is all to play for in the last five weeks of the campaign. One of their leading lights, former Conservative Defence Secretary Liam Fox, is highlighting what he regards as a powerful weapon for the Leave campaign. He has dubbed this the Strange Case of the Missing Veto.

In an interview for Newsnight, the former defence secretary said that people have overlooked a crucial element of David Cameron's deal with fellow EU leaders in February which prompted the prime minister to trigger the referendum.

This was Mr Cameron's decision to relinquish the UK veto if eurozone leaders eventually decide to underpin new governance arrangements for the single currency in a revision of the Lisbon treaty.

Britain, along with every other EU member state, has the right to veto any EU treaty revision. But in exchange for the concessions he won from fellow EU leaders in February, the prime minister said he would put away the famous Thatcher handbag and actually go further by supporting further integration in the eurozone.

Mr Fox told me this is a profound mistake which will weaken the UK's hand in the EU.

"Even if there is something that is harmful to the UK's interests we have already agreed in advance to implement it. That is what it is to be a sitting duck or at least that is what it will be if we choose to remain in the EU.

"What we have done ahead of this next treaty is we have written a blank cheque to Europe that said you you can put on that anything you want and we will guarantee to cash it," he said.

The former defence secretary told me he will accept the result of the referendum if the Leave side loses.

But some eurosceptics are planning to use the forthcoming Tory leadership contest to join battle again on Europe if the Remain side wins. When leadership hustings are held the eurosceptics want to ask the candidates a simple question: will you restore the UK veto?

A candidate would be brave to dismiss that question, raising hopes among the eurosceptics that they could unpick the prime minister's EU deal. If the next Tory prime minister pledged to restore the UK veto, EU leaders would probably say that the special deal for the UK had been thrown into question.

It would be difficult to unravel the prime minister's EU deal because it has been lodged at the UN and is said by Downing Street to be legally binding. But some eurosceptics are hoping that a challenge to the deal in Brussels could be one of number of triggers that could eventually lead to a second referendum.

One Brexit supporter says such eurosceptics are wrong. James Cleverly, the Tory MP for Braintree who is close to Boris Johnson, said that all Tories should accept the result - Leave or Remain - and then support the prime minister.

He told me: "I disagree fundamentally on this. This referendum is a one off vote. People should recognise that and take that vote seriously.

"The message I would say to Nigel Farage and anyone else who is thinking about a second referendum or neverendum is if we go back to the British people and say you seemed a little bit equivocal on that I strongly suspect they would come back with the same result but louder.

"They will say to us you clearly weren't listening the first time. This is what we told you, get on with it."

There will be intense speculation over the coming weeks about various possible outcomes after the referendum. Perhaps some of this thinking will include what Mr Fox hopes will soon be on everyone's lips: the Strange Case of the Missing Veto.