THERESA May today confirmed that Britain could stay tied to the EU for even longer - but insisted it would "only be for a matter of months".

The PM has faced a furious backlash from her own MPs worried about a further delay to Brexit.

The plan could cost the UK as much as £16billion as we continue to contribute to the Brussels budget, according to top Tories.

Arriving for the second day of the European Council summit, Mrs May claimed the proposal would only be an emergency measure to avoid a hard border in Ireland.

She told reporters: "A further idea that has emerged, and it is an idea at this stage, is to create an option to extend the implementation period for a matter of months, and it would only be for a matter of months.

"The point is that this is not expected to be used because we are working to ensure that we have that future relationship in place by the end of December 2020.

"In those circumstances there would be no need for any proposal of this sort and I'm clear that I expect the transition period to end at the end of December 2020."

During the transition period, Britain will continue to be treated as if it's a member of the EU even though we are officially leaving in March next year.

That will mean paying in to the EU budget and remaining part of the single market and customs union - meaning continued free movement of people, and a ban on cutting new trade deals around the world.

Yesterday Eurocrats asked Mrs May if she would consider extending the planned transition until December 2021, a year longer than previously pencilled in.

The idea is to give both sides longer to thresh out a hi-tech solution to the Irish border issue which would take away the need for checks on the island of Ireland or in the Irish Sea.

But after the PM signalled she may be open to the idea, Tory MPs hit out at the "desperate" ploy - and even called for her to quit.

Leading moderate Nick Boles, who backed Remain in the 2016 referendum, warned Mrs May she is shedding support from her party.

He told the BBC: "I'm afraid she is losing the confidence now of colleagues of all shades of opinion, people who have been supportive of her throughout this process.

"They are close to despair at the state of this negotiation because there is a fear that both the Government and the European Union are trying to run out the clock, that they are trying to leave this so late that they can credibly say there is no alternative but a no-deal Brexit and most people agree that would be chaos.

"That is not an acceptable way for a leader of a government to behave."

He claimed another year of transition would cost the Treasury nearly £16billion in additional payments to Brussels.

Brexiteer Nadine Dorries called on the PM to quit rather than make more concessions to Brussels.

She tweeted: "If Theresa May is asking for a longer transition period, she is stalling. It’s time to stand aside and let someone who can negotiate get on with it and deliver."

Another senior Tory told The Sun: "There are now 10billion reasons why Mrs May should go - this is not delivering the referendum in any way shape or form.

"Think what that £10billion could be spent on at home, police, schools, more doctors. It's a shambles."

And Remainers also mocked Mrs May - Labour's Gareth Thomas from the pro-EU Best for Britain campaign said: ""The Prime Minister can give herself as much Brextra time as required but it's not going to work.

"The Northern Ireland border issues are significant and the stark reality is that buying a few months or even another year, albeit welcome, will not solve the problem in itself."

The PM's de facto deputy David Lidington said a longer transition was "in the mix" but refused to confirm how much an extension would cost Britain.

He said the price tag would have to be "teased out" during further talks with Brussels.

Arriving for the second day of the European Council summit, Luxembourg's PM Xavier Bettel said time was running out for a Brexit deal and claimed Mrs May is under "huge pressure".

He said: "On March 29, it's game over. March 29 is the last day when the UK is a member of the EU so we have to have a deal before.

"We know Theresa May is in a tricky situation because she has got huge pressure in the UK and at Westminster."

Ex-ministers including Boris Johnson, David Davis and Iain Duncan Smith last night wrote to the PM calling on her to ditch her Chequers proposals or risk a humiliating "surrender" to Brussels.

They said: "We urge you to make clear that you will not bind the UK into the purgatory of perpetual membership of the EU's customs union, whether by a backstop or any other route.

"Talk of either a UK or a Northern Irish backstop is inimical to our status as a sovereign nation state."