Jeremy Hunt says Remain campaigners are almost two thirds of the way to killing Brexit.

The Foreign Secretary says that if Theresa May's deal is defeated then the country could be heading for a second referendum.

He also warns that Britain may end up "in the customs union by the front door."

Hunt's intervention comes as aides to the prime minister discuss forcing her out in order to win support for her deal.

LONDON — The campaign to prevent Brexit is almost two thirds of the way to succeeding, the Foreign Secretary Jeremy Hunt said on Sunday.

Speaking on the Andrew Marr show, Hunt said "there is wind in the sails of those trying to prevent Brexit," adding that there was now a real "possibility that we end up losing Brexit... in the next couple of weeks."

The House of Commons will on Tuesday vote for a second time on Theresa May's Brexit deal in what is expected to be another historic defeat for the UK government.

If defeated, May has committed to holding a vote on delaying Britain's exit from the EU beyond the current March 29 deadline, leading to renewed hopes from Remain campaigners that Brexit could be prevented.

"If you want to stop Brexit, you only need to do three things," Hunt said.

"Kill this deal, get an extension and then have a second referendum.

"Within three weeks those people could have two of those three things... Quite possibly the third one could be on the way through Labour Party."

He added: "There is a risk and a possibility that we end up losing Brexit if we get the votes wrong in the next couple of weeks."

He also warned that Britain could end up with a significantly softer Brexit with the country could "end up in the Customs Union by the front door."

Responding to Hunt's comments, the deputy chairman of the pro-Brexit European Research Group of Conservative MPs, Steve Baker, said in a statement:

"The people who would stop Brexit should know just this: what you do, you’ll have [to] do in public now.

"And everyone will know just what you have done.

"Stopping Brexit will be on you, not Brexiteers. Don’t kid yourselves otherwise."

The Labour party has given its conditional support to holding a second referendum on leaving the EU, but only if attempts to secure a Brexit deal on terms more favourable to the party, fails.

Shadow Chancellor John McDonnell told the programme that the option would remain "on the table."

He also said the party would support an extension to the two-year Article 50 process that will take Britain out of the EU.

Asked how long any extension should be, he replied that the delay would be "as long as necessary."