The Irish border backstop is not on the table for re-negotiation, Leo Varadkar has said.

Ireland’s Taoiseach held a lengthy one-to-one meeting with Theresa May ahead of the main European Council summit of leaders in Brussels on Thursday.

He said that while the EU was keen to assist the Prime Minister, it could not reopen the Withdrawal Agreement.

Mr Varadkar said: “As the European Union we are very keen to offer explanations, assurances, clarifications, anything that may assist MPs to understand the agreement and hopefully to support it but the backstop is not on the table.”

He reiterated: “If the backstop has an expiry date, if there is a unilateral exit clause, then it is not a backstop. That would be to render it inoperable.

“That would mean reopening the substance of the Withdrawal Agreement and the European Union is unequivocal that is not an option.”

Mrs May is seeking reassurances about the backstop, an insurance policy if nothing better is on offer which neither side are seeking.

It would mean Northern Ireland remaining aligned to EU regulations after Brexit to prevent a hard border with the Republic.

The backstop has been opposed by unionists over fears it could split Northern Ireland from the rest of the UK.

Critics believe it could leave the UK bound by EU rules indefinitely, restricting the ability to strike trade deals with other countries.

Mr Varadkar said the deal negotiated last month between Britain and the EU was the only one available.

BrexitLeo Varadkar said the deal negotiated last month between Britain and the EU including the Irish border backstop was the only one available (Niall Carson/PA)

Mrs May has said she is not expecting a breakthrough on the backstop during this week’s two-day summit in Brussels.

European leaders have said any assurances they deliver cannot contradict the accord agreed with the Prime Minister.

Earlier this week the Taoiseach raised the prospect of delaying next March’s Brexit to allow a resolution.

Ireland is stepping up its preparations for a no-deal Brexit with additional measures at ports and airports but not at the land border with Northern Ireland.

Mr Varadkar’s meeting with the Prime Minister scheduled for Wednesday evening in Dublin was cancelled due to the Tory no-confidence vote.