Taoiseach Leo Vardakar has set out a second key condition for acceptance by Ireland of any Brexit backstop review mechanism currently being proposed by the UK.

The review mechanism discussion is understood to be critical to breaking the talks impasse ahead of the United Kingdom’s exit from the European Union in March 2019.

Speaking in Helsinki, Finland on Wednesday, Mr Varadkar said any review mechanism could not be unilateral on the part of the UK. Secondly, he said it would have to be based on a sufficiently ambitious “future relationship” agreement being in place to “achieve the same objective, which is that there be no hard border between Northern Ireland and Ireland.”

Theresa May’s cabinet could meet later this week to sign off on a proposal for the review mechanism to determine how Britain could exit a backstop after Brexit. Mrs May told ministers on Tuesday that she wanted a withdrawal deal with the EU as soon as possible but not at any price. EU negotiators believe there must be movement on the backstop by the end of this week if there is to be a special summit to approve the withdrawal deal before the end of this month.

Britain has previously committed to having a backstop in place which would act as an insurance policy in the event of a no-deal Brexit so that the Irish border stays open.

During a cabinet meeting that lasted almost three hours, every minister contributed to a discussion of the Brexit negotiations which focused on the backstop. Attorney general Geoffrey Cox described the EU’s willingness to consider a review mechanism for the backstop as a “major step” towards a deal.

Mr Cox is understood to have told ministers that a mechanism based on mutual consent could offer Britain the same certainty as a unilateral mechanism favoured by Brexit secretary Dominic Raab.

Mr Varadkar, who spoke to Mrs May about a review mechanism on Monday, has ruled out a unilateral option.

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Wednesday’s intervention by Mr Varadkar that any review can only be taken in the context of another agreement that guarantees the same outcome as the backstop may prove to be a further stumbling block in reaching a withdrawal deal by the end of November.

Mr Varadkar said the review mechanism “can’t be one that would allow the UK to resile unilaterally from its commitment that there should be no hard border in Ireland. His comments set a high bar for any future relationship agreement.

Mr Varadkar, echoed by the Finnish Prime Minister and a growing consensus on the talks timeline, also said that it was now more likely that a deal on the Brexit withdrawal agreement would be done ahead of the December summit.

“I do think that every day that passes,” he said,”the possibility of getting a special summit in November becomes less likely but we do have one scheduled anyway for the 13th of December.

“So not getting it done in November doesn’t mean we can’t get it done in the first two weeks of December, but beyond that we’d be into the New Year but that wouldn’t be a good thing.”

The Taoiseach is in Helsinki for the conference of the European People’s Party to which Fine Gael is affiliated. The conference, attended by over 2,000 delegates and many EPP heads of state is due on Wednesday to agree to the party’s candidate for the Commission presidency for the European Parliament elections next year.

Mr Varadkar held a bilateral with Finland’s Prime Minister Juha Sipila in the latter’s scenic, shoreside residence, Kesaranta, and spoke to journalists after the meeting.

Speaking on the negotiations on the backstop and the nature of a proposed review process, Mr Varadkar said that “For me it’s always about the objective – what are you trying to achieve. What we’re trying to achieve is a guarantee that a hard border won’t emerge between Northern Ireland and Ireland and the backstop is part of that.

“We hope that the backstop will never need to be used. It is an insurance policy and we hope that if it has to be used it will only be temporary, but in order for the backstop to be a backstop if it is ever invoked it must apply unless and until a new agreement supersedes it and achieves the same objective which is that there be no hard border between Northern Ireland and Ireland.

“And that’s a commitment that was there from December ... and now we need to get that written into the text in the withdrawal agreement,” the Taoiseach said.

“As I said yesterday in the Dáil, I think that in order to come to agreements .... you have to be willing to come up with creative solutions and be creative about language .... it [a review process] can’t be one that would allow the UK to resile unilaterally from its commitment that there should be no hard border in Ireland.”

Asked if he would have difficulty urging voters next year to back the party of Hungary’s Viktor Orban or Italy’s Silvio Berlusconi, Mr Varadkar insisted that all European parties were broad churches, “umbrella parties”.

Fianna Fáil’s Liberal group – “ strange that FF is in the Liberal group, but they are” — after all includes the Czech ANO “with policies very similar to Mr Orban in Hungary and of course many of the people in the social democratic parties used to be car-carrying and practising communists ....”

“I’m not asking people to vote for these parties when people vote in the European elections in Ireland,” Mr Varadkar said, “I’m asking them to vote for Fine Gael and for the EPP, to vote for our policies and values of the EPP ... liberal democracy, Christian democracy... We are the people who saw off communism in Europe and saw off fascism .”