Theresa May has told MPs there may be limited circumstances when it is in Britain’s interest to agree to a short extension to the transition period after it leaves the EU in March 2020.

In a Commons statement following last week’s EU summit in Brussels, the Prime Minister said such an extension would be an alternative to activating the so-called Northern Ireland “backstop”, intended to guarantee there is no return to a hard border with the Republic.

She stressed that in any circumstances the transition – currently due to end at the end of 2020 – would have to be over “well before” the end of the parliament expected in June 2022.

“There are some limited circumstances in which it could be argued that an extension to the implementation period might be preferable, if we were certain it was only for a short time,” she said.

“For example, a short extension to the implementation period would mean only one set of changes for businesses – at the point we move to the future relationship.

“But in any such scenario we would have to be out of this implementation period well before the end of this parliament.”

Mrs May faced a furious response from some Tory MPs after it emerged that the possibility of an extension to the transition period – currently due to run for 21 months – had been discussed by EU leaders in Brussels.

It prompted accusations the UK could be forced to pay billions into EU coffers for months – or even years – to come after it has left bloc.

The Prime Minister said while the terms of the withdrawal agreement were now 95% agreed, there remained an “impasse” over the issue of the Irish border.

She made clear, however, she would not accept a situation in which the UK could be kept “indefinitely” in either an extended period of transition or a backstop which tied the UK to EU customs rules.

“We would not accept a position in which the UK, having negotiated in good faith an agreement which prevents a hard border in Northern Ireland, nonetheless finds itself locked into an alternative, inferior arrangement against our will,” she said.

BrexitJeremy Corbyn has said the Government has been forced to seek a Brexit extension due to its own incompetence (PA)

Labour leader Jeremy Corbyn said the Government had been forced to consider extending the transition period as a result of “its own incompetence”.

“The Conservative Party has spent the last two years arguing with itself instead of negotiating a sensible deal in the public interest,” he said.

“Their Brexit negotiations have been a litany of missed deadlines, shambolic failure and now they’re begging for extra time.”

There was some respite for the Prime Minister as leading Tory Brexiteer Steve Baker announced he was withdrawing amendments to the Northern Ireland Bill intended to prevent the backstop being implemented.

In the Commons, Mrs May reiterated the Government could not accept the original EU backstop plan as it would create a “customs border down the Irish Sea”, breaking up the integrity of the UK.

Earlier Downing Street slapped down anonymous Conservative MPs who used violent imagery to describe a possible coup to unseat Mrs May.

Weekend newspapers reported Tory backbenchers saying the Prime Minister would be “knifed” and she should “bring her own noose” to a meeting with MPs to discuss her Brexit plans.

The PM’s official spokesman said Mrs May expected those in public life to avoid “dehumanising” and “derogatory” language.

BrexitIain Duncan Smith has denied undermining the Government’s negotiating position (Jonathan Brady/PA)

“I don’t intend to dignify those specific anonymous comments with a response,” the spokesman told a regular Westminster media briefing.

“The Prime Minister has always been very clear that we must set a tone in public discourse that is neither dehumanising nor derogatory.

“Personal vitriol has no place in our politics.”

The vicious attacks marked the start of what is expected to be a tough week for the Prime Minister, with some observers speculating that the number of MPs calling for her removal may reach the 48 figure which would trigger a vote of no confidence.

Mrs May spoke with Cabinet colleagues in lengthy telephone conference calls over the weekend, which Downing Street described as a chance to “give an update on the negotiations”.

Meanwhile former Cabinet ministers Iain Duncan Smith and Owen Paterson denied undermining the Prime Minister after meeting the EU’s chief Brexit negotiator, Michel Barnier, in Brussels.

Mr Duncan Smith said: “We are presenting some ideas which we think are constructive and we had a constructive discussion.

“Now we are going to go back and talk to the Government about it.”

He added that whoever briefed in violent terms about the Prime Minister’s future “needs to have the fullest weight of the Conservative Party upon them”.

“It has nothing to do with our politics, it has nothing to do with this issue,” he told reporters in Brussels, adding Mrs May had his “full support”.