The UK could remain tied to Brussels’ rules beyond the end of 2020 to give negotiators more time to finalise a trade deal, according to reports.

The potential extension of the transition period, which would see the UK stay in the EU single market and customs union, is being considered as intensive negotiations continue ahead of a crunch summit in Brussels on Wednesday.

Under the current plans, if there is a Brexit deal the transition period will last until the end of 2020, during which the UK will accept Brussels’ rules without having a seat at the table when they are decided.

Dominic Raab said any backstop customs arrangement would have to be 'finite' (Aaron Chown/PA)
Dominic Raab said any backstop customs arrangement would have to be ‘finite’ (Aaron Chown/PA)

But the Guardian and Daily Telegraph reported that the option of a potential extension was being considered by negotiators in Brussels to allow extra time to drawn up a deal on the future UK-EU relationship – and avoid the need to use a controversial “backstop” arrangement to avoid a hard border between Ireland and Northern Ireland.

The Department for Exiting the European Union said it would not comment on speculation.

The need to resolve the backstop issue is a political headache for Theresa May.

The European Union’s version, which would see just Northern Ireland remain aligned with Brussels’ rules, has been called unacceptable by Mrs May and is fiercely resisted by her Democratic Unionist Party allies.

Mrs May’s counter-proposal, set out in June, was for a “temporary customs arrangement” for the whole UK, but Tory Brexiteers are suspicious this could turn into a permanent situation – restricting the freedom to strike trade deals around the world.

Brexit Secretary Dominic Raab said that a provision on customs which was not “finite” would fail to deliver the result of the 2016 referendum.

And Downing Street insisted that Mrs May would never agree a Brexit deal with the EU which “traps” the UK permanently in a customs union.

The pledge came amid speculation over possible ministerial resignations if the Prime Minister gives too much ground ahead of the Brussels summit next week.

Mr Raab said: “What we cannot do is see the UK locked in via the back door to a customs union arrangement which would leave us in an indefinite limbo. That would not be leaving the EU.”

However, the EU is mounting resistance to any specific time limit being included in the text of the UK’s Withdrawal Agreement.

Irish Foreign Minister Simon Coveney insisted the backstop should be able to remain in place “unless and until something better comes along” and told ITV News it was a “deal breaker”.

Chancellor Philip Hammond became the first senior Government figure to suggest that the backstop – designed to keep the border between Northern Ireland and the Republic open in the case that no broader EU/UK trade deal is finalised – will “probably” have to come into effect for a period.

Nigel Dodds, deputy leader of the Democratic Unionist Party which props up Mrs May’s minority Conservative administration in the House of Commons, said he expected developments over the weekend “in terms of the Government’s own position and the Cabinet”.

Stewart Jackson, who was chief of staff to ex-Brexit secretary David Davis, said it was “quite possible” that another Cabinet minister could follow the example of his former boss and resign.

He told BBC’s Newsnight: “Political resignations are part of the landscape.”

Brexit was a “fundamental, existential issue” and “on that basis maybe some people will obviously consider their position”, he said.

Meanwhile, pro-EU Tory MPs faced a campaign orchestrated by insurance tycoon and Leave.EU founder Arron Banks – although he insisted the funding came from Brexit-supporting small donors.

The Blue Wave is targeting a “Dirty Dozen” of Conservatives, including an “an epic constituency-wide maildrop in Folkestone” – the seat of Damian Collins, the chairman of the Culture, Media and Sport Committee who has clashed with Mr Banks.

Asked if he was trying to “put the frighteners” on the MPs, Mr Banks told Channel 4 News: “Well there is an element of that, I’m not going to deny that.”

Mr Collins said: “He can send as many letters as he likes, I won’t stop doing my job.”

Fellow Tory MP Antoinette Sandbach said she would not be “bullied” by Mr Banks.

Arch Brexiteers will gather in Torquay for a Leave Means Leave rally on Saturday which will see Tory Jacob Rees-Mogg share a stage with former Ukip leader Nigel Farage.

Mr Farage said: “The Government’s Brexit Betrayal is getting worse by the day.

“We at Leave Means Leave are going to build national branches all over the country to fight for democracy from grassroots level and to deliver the Brexit that people voted for.”