Divisions at the top of the Conservative Party over Europe were laid bare as senior ministers clashed over whether the reform deal secured by David Cameron will be legally binding on European courts.
Justice Secretary Michael Gove and justice minister Dominic Raab insisted that the European Court of Justice would not be bound by the agreement, which was being lodged with the United Nations on Wednesday.
But Downing Street said that registering the agreement with the UN "put beyond doubt the fact that it is legally binding and irreversible in international law", while the Government's senior law officer, Attorney General Jeremy Wright, insisted that the ECJ "must take it into account".
The row came as Number 10 was forced to apologise to special forces general Sir Michael Rose after incorrectly including his name in a letter from senior military commanders warning that Brexit posed a threat to security.
Sir Michael complained after finding his name on the letter to the Telegraph, in which a group of former senior military commanders said leaving the EU could hamper the UK's ability to tackle threats such as Islamic State or Vladimir Putin's Russia. Downing Street, which arranged the letter, blamed "an administrative error".
Meanwhile, the head of the International Monetary Fund warned that British withdrawal would be bad for both the UK and the EU.
Christine Lagarde told CNN: "My hunch ... is that it is bound to be a negative on all fronts. For those that stay, because there are fewer of them, and for those who go, because they lose the benefit of [that] facilitation of exchange."
As Mr Gove made his first major intervention in the referendum campaign since backing Brexit, his wife Sarah Vine wrote in her Daily Mail column that he had been "locked in an internal struggle of agonising proportions", but had chosen "own heartfelt beliefs" over "loyalty to his old friend, the Prime Minister".
The Justice Secretary insisted the EU has held Britain back and said the nation would recover its "mojo" outside the 28-member bloc.
Mr Gove said the failure of the single currency and problems with migration showed the EU was an "old-fashioned model".
"I think it would be a tremendous opportunity for Britain to recover its mojo, for Britain to be a more flexible, outward-looking, creative place," he told the BBC.
"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."
On the legal force of the reform package, Mr Gove insisted that Mr Cameron had not misled voters, but added: "The European Court of Justice stands above every nation state, and ultimately it will decide on the basis of the treaties and this deal is not yet in the treaties."
Justice minister Dominic Raab backed his departmental boss, saying: "This is not the kind of legal guarantee you get when you buy a dishwasher, so you get your money back if it breaks down. Ultimately, it is crystal clear the Luxembourg court will have the last word as to what sticks, and it is free to not enforce the British deal."
But Mr Wright insisted the deal "has legal effect from the point the UK says it intends to remain in the EU, and the European Court must take it into account".
"The job of the European Court is to interpret the agreements between the 28 nation states of the EU," said the Attorney General. "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."
Asked whether Mr Cameron continued to have full confidence in a Justice Secretary whose judgment on a point of law was at odds with that of the Government's most senior legal advisers, a Downing Street spokesman replied: "Yes, he does."
The Downing Street interpretation was backed by European Council president Donald Tusk, who told the European Parliament the package was "legally binding and irreversible" and "cannot be annulled by the European Court of Justice".
Mr Tusk poured cold water on suggestions that the EU might offer a better deal if the UK votes to leave on June 23, telling MEPs: "The European Union will respect the decision of the British people. If the majority votes to leave, that is what will happen. It will change Europe forever and it will be a change for the worse."
And EU Finance Commissioner Lord Hill said there was "clear legal advice" that this a "fully binding legal agreement".
He told BBC Radio 4's World At One programme: "It's the case that the ECJ has never overturned a clearly expressed binding agreement given by all 28 leaders."
European Commission president Jean-Claude Juncker described the deal as "fair", telling MEPs:"The UK Prime Minister got the most he could obtain and the other member states offered him as much as they could offer."
Guy Verhofstadt, leader of the Alliance of Liberals in Democrats in Europe, said Mr Cameron and London Mayor Boris Johnson were engaged in a "glorified cock-fight".
"I have seen ambitious politicians ... but Boris Johnson takes it to a whole other level, because he is the Mayor of London acting against the interests of the citizens of London from personal ambition, and certainly not for a better Europe and a better Britain," the former Belgian Prime Minister told MEPs. "It's bonkers."