Boris Johnson in race against time to persuade MPs to back his Brexit deal

Downing Street will launch a charm offensive as it attempts to win Parliament's backing for Boris Johnson's new Brexit deal.

The Prime Minister must win the support of at least 320 MPs when the agreement is voted on in the Commons on Saturday.

If he fails, it is understood the Government will launch a fresh bid to hold a general election.

Speaking in Brussels after EU leaders signed off on the new deal, Johnson said: "I am very confident that when my colleagues in Parliament study this agreement that they will want to vote for it on Saturday and in succeeding days."

But his job has been made harder by the fact that the Conservatives' confidence and supply partners in the DUP - who Number 10 spent days trying to woo - have said they cannot vote for the deal.

They are furious that measures which will see Northern Ireland remaining tied to the EU customs rules can remain in place so long as they have majority support in the Stormony Assembly.

DUP deputy leader Nigel Dodds said: "[Boris Johnson] has been too eager by far to get a deal at any cost and the fact of the matter if that if he had held his nerve he would have got better concessions."

But the PM has been boosted by the fact that senior members of the European Research Group of Tory Brexiteers, who consistently voted against Theresa May's Brexit deal, have said they are willing to back the new agreement.

The majority of the 21 Tory rebels sacked by the Prime Minister for backing the Benn Act have also said they will vote for the deal.

Oliver Letwin said said the new deal "looks admirable, and I shall be supporting it, and indeed voting for the implementation of it in legislation all the way to completion".

And Sir Nicholas Soames told the BBC's Newsnight programme: "It’s been a very painful time – not just for parliament, but for the country. Families have split. Businesses have split. The country is split, which is why Parliament is split.

"And it is, therefore, time, I think to say that this is the end of a very painful time. We have a deal, we now need to get that scrutinised and put it to proper legislation and through the House of Commons."

Johnson must also try to woo Labour MPs from Leave-voting areas who have previously said they will vote for a deal.

However, Labour insiders believe that fewer than 10 of them will end up backing the Prime Minister.

A Downing Street spokesman said: "Tomorrow will be a defining opportunity for Parliament - an opportunity to come together and get Brexit done.

"MPs will be able to honour the referendum they pledged to implement, they can deliver on the manifesto promises they made and they can help this country move on.

"It doesn’t matter whether you voted leave or remain, it doesn’t matter what rosette you wear, its time to get Brexit done  and deliver on the public’s priorities."