MICHEL Barnier has issued a fresh warning to Britain that it must "settle the accounts" if it wants a free trade deal with the European Union after it leaves the bloc in 2019.

Speaking on the eve of a keynote speech by Theresa May in Florence tomorrow, the EU’s chief negotiator said there was still "major uncertainty" over the UK's approach on key issues.

"All that is necessary in this negotiation is that everyone honours the commitments that they have made to each other; to settle the accounts; no more, no less," declared Mr Barnier.

"Beyond money, this is a question of trust between the 27 and the United Kingdom based on the respect of one's signature. Everyone knows that we will need this trust to create a solid relationship in the future," explained the EU chief negotiator.

Speaking in the Italian Parliament, Mr Barnier added that he would be listening "attentively and constructively" to what the Prime Minister had to say tomorrow.

Earlier today, Mrs May briefed her colleagues in a marathon session of the Cabinet. Members got half an hour to digest the 5,000-word speech before they discussed it with the PM in the chair for another two hours.

It is believed Mrs May will make an “open and generous offer” to the EU but will not mention the mooted £17 billion figure, which officials have privately suggested the UK might be willing to pay to “settle its dues” to the EU and help ease access to the single market during a two-year transition period.

Just before lunch, Cabinet ministers emerged into Downing Street with Philip Hammond and Boris Johnson - who have been at loggerheads all summer over Brexit – leaving together in a show of public unity.

But the difference of approach between the two senior figures appears difficult to bridge. The Chancellor favours a Swiss-style deal in which Britain would continue to pay for access to the single market while the Foreign Secretary wants a looser arrangement along the lines of the EU's free trade agreement with Canada.

Mrs May sits somewhere in the middle, insisting it is not a "binary" choice and she would be seeking a "bespoke" arrangement for the UK rather than following a pre-existing, "off-the-shelf" model.

Mr Hammond and Mr Johnson together with David Davis, the Brexit Secretary, will be in the audience when the PM speaks tomorrow in Italy.

The last few days have been dominated by the row caused by Mr Johnson’s 4,222-word article on Brexit, which Ruth Davidson, the Scottish Conservative leader, denounced as badly timed given the Parsons Green Tube bombing, and Amber Rudd, the Home Secretary, criticised as “back-seat driving” on Britain’s EU withdrawal.

As the prospect of the Foreign Secretary was talked up and then talked down, Mr Johnson declared that he was “mystified” by the row, which he dismissed as a “snore-athon”.

He has let it be known that he believes the UK will have to “settle its dues” to the EU but should not have to pay for access. He has also dismissed the notion of Britain signing up to the European Economic Area as this would make Britain a “vassal state”; paying for membership of a body but having no control over its rules or decisions.

Yet in a sign of the continuing divisions at the top of the Conservative Party, Nick Timothy, Mrs May's former chief of staff, used a column in The Daily Telegraph to accuse Mr Hammond of failing to promote the positives of Brexit.

He said the Treasury had failed to emphasise the "opportunities of Brexit" and accused the Chancellor of being on "manoeuvres".

Calling for unity, he said: "Boris Johnson and Philip Hammond - who has also been on Brexit manoeuvres this summer - must understand that the surest route to a bad deal, or no deal at all, is to go on behaving as they are."