INFIGHTING at the top of the Conservative Party intensified today after Michael Gove insisted David Cameron’s EU deal was not legally binding as claimed but a former Attorney General said the Justice Secretary was wrong and should consult his departmental lawyers.

In the most divisive intervention from the top of the UK Government so far in the EU campaign, Mr Gove rejected the Prime Minister's insistence that the package of reform was legally binding and irreversible, warning that the European Court of Justice was not bound by the settlement without treaty change.

As the Scot, one of several Cabinet ministers backing Brexit, clashed with his friend and colleague Mr Gove’s wife, journalist Sarah Vine, told of the "agonising" struggle he had faced as her husband put his Euroscepticism ahead of his close friendship with Mr Cameron.

The Cabinet minister insisted the EU had held Britain back and said the nation would recover its "mojo" outside the 28-member bloc.

Despite his view on the legal nature of the deal with Brussels, the Secretary of State insisted the PM, who has claimed the deal is "already legally binding and irreversible", had not misled voters.

But he told the BBC: "The facts are that the European Court of Justice is not bound by this agreement until treaties are changed and we don't know when that will be.

"He's absolutely right that this is a deal between 28 nations, all of whom believe it. But the whole point about the European Court of Justice is that it stands above the nation states.”

Mr Gove stressed it was important for people to recognise the European court stood above every nation state and ultimately would decide on the legality of the deal based on EU treaties and that the deal was not yet in the treaties.

The minister, whose key role is to oversee the criminal justice system in England, said the failure of the single currency and problems with migration showed the EU was an "old-fashioned model".

"It would be a tremendous opportunity for Britain to recover its mojo, for Britain to be a more flexible, outward looking, creative place. One of the big problems with the European Union is that it has held us back."

He added: "The nature of the European Union is bureaucracy. The failure of the single currency, the problems that it has had with migration, all of them point to the fact that it is an old-fashioned model. It's sclerotic, it's out of date."

But Downing Street was swift to defend the PM’s deal, secured at a marathon summit in Brussels, as legally binding and irreversible.

“Britain's new settlement in the EU has legal force and is an irreversible international law decision that requires the European Court of Justice to take it into account," said a No 10 spokesman.

Dominic Grieve, the former Attorney General, said it was "fanciful" to say the deal did not have force in law.

“Michael Gove is wrong about this,” the Berkshire MP told the BBC. “It is quite plain…the agreement that we have reached has legal force. It will have legal force from the day on which we indicated after a referendum that we wish to stay in the European Union. And thereafter the terms of the agreement can be raised in any court case where it is relevant, and the court would have to take it into account.”

When it was suggested “take it into account” did not mean being bound by the agreement, Mr Grieve replied: “All courts have to take into account and be bound by what is said. I think this is a bit of an exercise in semantics. Ultimately, Michael Gove’s problem appears to be that he just doesn’t trust the court.”

He added: “All I can say, I can’t comment as to why Michael Gove has said what he does, I suggest that Michael Gove should consult his own departmental lawyers, who would be able to enlighten him as to the status of the agreements.”

Jeremy Wright, the current Attorney General, echoed his Tory colleague, saying Mr Gove’s assertion was incorrect and the agreement would have legal effect from the moment the UK voted to remain in the EU.

He explained: "The job of the European Court is to interpret the agreements between the 28 nation states of the EU. This is one of those agreements with equivalent legal force to other agreements such as treaties.

"That is not just my opinion - it is the opinion of this Government's lawyers, lawyers for the EU, and, I suspect, the majority of lawyers in this country," he added.

Meantime, Martin Schulz, President of the European Parliament, noted how exempting Britain from ever closer union would be "written exactly literally like it is" in the deal in future treaty change.

Asked if welfare curbs would deter migrants from moving to Britain, he replied: "I don't believe so."

Mr Schulz added: "For the first time since a long time a Conservative Prime Minister of the United Kingdom is fighting for Europe and for the European Union. This is a progress in itself."

Elsewhere, a group of former senior military commanders have warned that leaving the European Union could hamper the UK's ability to tackle threats such as Islamic State or Vladimir Putin's Russia.

In a letter to the Daily Telegraph, the ex-services chiefs told of their concern about the rise of IS, also known as Daesh, saying: "We are proud to have served our country and to have played our part in keeping Britain safe. In the forthcoming referendum, therefore, we are particularly concerned with one central question: will Britain be safer inside the EU or outside it? When we look at the world today, there seems to us only one answer.”

They wrote that Europe today was facing a series of grave security challenges; from instability in the Middle East and the rise of so-called Islamic State to resurgent Russian nationalism and aggression.

"Britain will have to confront these challenges, whether it is inside or outside the EU. But within the EU, we are stronger. Inside it, we can continue to collaborate closely with our European allies, just as we did when we helped to force the Iranians to the negotiating table through EU-wide sanctions, or made sure that Putin would pay a price for his aggression in Ukraine," added the ex-services chiefs.

Signatories to the letter, which was in part co-ordinated by Downing Street, included former chiefs of defence staff Field Marshal Lord Bramall and Field Marshal Lord Guthrie.

Air Chief Marshal Lord Stirrup, Admiral of the Fleet Lord Boyce and former special forces chief General Sir Michael Rose are also among the 13 senior officers who backed the letter.

In a further development, new research has suggested high levels of Euroscepticism among British voters might not translate into a vote to leave the EU on June 23.

Fears of the impact of Brexit on the UK economy could explain the reluctance of some voters to convert their dissatisfaction with Europe into a vote to Leave, the 2015 British Social Attitudes survey indicated.

Some 22 per cent of those questioned said they wanted to leave the EU and 43 per cent said the Union's powers should be reduced; a level of Euroscepticism which has been topped only once since 1992 in the regular survey.

But despite this widespread concern about the EU, a clear majority of those questioned, 60 per cent, said the UK should continue to be a member with just 30 per cent saying it should withdraw.

Just 24 per cent of those questioned by pollsters NatCen Social Research felt the British economy would be better off outside the EU compared to 40 per cent who said it would be damaged.