Theresa May has indicated she is ready to consider extending the UK’s transition out of the EU for an additional year to the end of 2021.

If agreed, the change would mean the UK remaining within the single market and customs union and subject to EU rules and regulations for almost three years after the official date of Brexit in March 2019 and more than five years after the referendum vote to leave.

Mrs May was fighting to preserve the possibility of a deal with Brussels on the UK’s withdrawal, after negotiations foundered last weekend on the intractable issue of the Irish border.

She addressed leaders of the 27 remaining EU member states in Brussels ahead of a dinner at which they discussed Brexit in her absence.

The president of the European Parliament, Antonio Tajani, who also spoke, said: “Both sides mentioned the idea of an extension of the transition period as one possibility which is on the table and would have to be looked into.”

A senior EU official later said Mrs May had indicated she was “ready to consider” a longer transition period.

Belgium EU Brexit
Theresa May arrives in Brussels to brief the remaining 27 EU leaders (European Commission Audiovisual Services)

Mrs May initially suggested an “implementation period” of around two years after Brexit, to give the UK’s authorities and companies time to prepare for the new arrangements.

But she later accepted a 21-month transition offered by the EU, ending on the last day of December 2020.

It emerged on Wednesday that the EU’s chief Brexit negotiator Michel Barnier was ready to discuss a further year’s extension to allow time to find a solution to keep the Irish border open.

UK officials stressed that the Prime Minister was not proposing any extension to the period already agreed.

Any further proposed extension is likely to be fiercely opposed by Eurosceptics, who warn the UK would become a “vassal state” of Brussels, bound by its rules but unable to influence them.

Theresa May and Jean-Claude Juncker
Mrs May was greeted in Brussels with a kiss from European Commission president Jean-Claude Juncker (European Commisison Audiovisual Services)

And it is likely to involve a demand from Brussels for a further year’s contributions towards EU budgets, which could cost the UK as much as £9 billion.

Before travelling to Brussels, Mrs May vowed to protect the “precious Union of the United Kingdom” as she answered questions in the House of Commons.

However, during exchanges at Prime Minister’s Questions, Labour leader Jeremy Corbyn said the Tories were too “weak and divided” to negotiate effectively with Brussels.

Mrs May told MPs: “We will not accept any proposals which would effectively break up the United Kingdom.”

The meeting in Brussels was supposed to be the occasion when the leaders of the EU 27 member states gave the green light for a special summit in November to finalise the terms of Britain’s withdrawal.

However, European Council president Donald Tusk has warned that without new “concrete proposals” from the British to break the logjam over the Irish border backstop, further progress on a deal may be impossible.

In a speech to the German parliament before travelling to Brussels, Chancellor Angela Merkel said that the possibility of a Brexit deal was “still there”, but added that Berlin was making plans for a no-deal withdrawal.

And in Paris, Emmanuel Macron’s government published details of legislation to authorise preparations for a no-deal Brexit, which could see the restoration of customs checks and health inspections for animals at French ports, and even a requirement for Britons to seek visas for stays of three months or more.