Theresa May is set to ask the European Union for an extra transition period that would see full Brexit delayed until around seven years after the vote to Leave.

Under the plans, briefed by government officials to The Times newspaper, the whole of the United Kingdom would stay aligned with EU regulations and customs procedures until 2023 to help avoid a hard border in Ireland. It comes on top of a two-year transition period from 2019 to the start of 2021 which has already been agreed.

The latest plan for a longer transition is intended as a replacement for the border “backstop” agreed by negotiators in December under which the UK would “maintain full alignment” with the single market if no other solution could be found, to remove the need for border checks.

Despite having been agreed in theory, that earlier policy now faces opposition from both the DUP and Brexiteers in the Cabinet – but for different reasons, and the UK Government now says it is “unacceptable” and will come up with new proposals.

The new plan, expected to be unveiled by the Government in early June, is extremely unlikely to be looked on favourably by Brussels – which says the backstop cannot be time-limited and must apply only to Northern Ireland.

The old “backstop” agreed in December originally looked like a done deal, but is now being interpreted in such different ways by the EU and UK that it is again a major barrier to concluding a withdrawal agreement.

Whatever backstop is agreed, it now looks increasingly likely to come into play on the Northern Ireland border – with no other solution to the customs conundrum on the horizon.

If it is necessary, it will be in a very limited set of circumstances for a limited time. Theresa May commenting on the Northern Ireland backstop earlier this week

If agreed, the new plan would effectively extend the Brexit process to at least seven years. Sir Ivan Rogers, the UK’s old ambassador to the EU, was criticised after he advised ministers in 2016 that leaving the EU would take around 10 years. He stepped down from his post shortly after.

The EU says under the December agreement just Northern Ireland would stay in full alignment with the single market and customs union to prevent a hard border, while UK negotiators say they actually agreed that the whole UK would do so. The relevant text is somewhat ambiguous as to what was agreed.

EU officials do not want the backstop to apply to the whole UK because it would give Britain access to the single market without having to uphold the so-called “four freedom” or submitting to the European Court of Justice. The UK says it cannot accept the backstop only applying to NI because that would create a potential customs border between Great Britain and NI – which the DUP oppose. Theresa May has relied on the DUP for her majority in the House of Commons since she called an election and lost seats last year.

The time-limiting element has now been introduced by the UK because Cabinet Brexiteers like Boris Johnson fear that an indefinite backstop could be a backdoor way of keeping the UK aligned with the EU in perpetuity. Ministers have publicly confirmed that a time-limited backstop is on the way.

Brexit threatens life on the Irish border: in pictures Show all 15 1 /15 Brexit threatens life on the Irish border: in pictures Brexit threatens life on the Irish border: in pictures An abandoned shop is seen in Mullan, Co Monaghan. The building was home to four families who left during the Troubles. The town was largely abandoned after the hard border was put in place during the conflict. Mullan has seen some regeneration in recent years, but faces an uncertain future with Brexit on the horizon Reuters Brexit threatens life on the Irish border: in pictures A defaced ‘Welcome to Northern Ireland’ sign stands on the border in Middletown, Co Armagh Reuters Brexit threatens life on the Irish border: in pictures Mervyn Johnson owns a garage in the border town of Pettigo, which straddles the counties of Donegal and Fermanagh. ‘I’ve been here since 1956, it was a bit of a problem for a few years. My premises has been blown up about six or seven times, we just kept building and starting again,’ Johnson said laughing. ‘We just got used to it [the hard border] really but now that it’s gone, we wouldn't like it back again’ Reuters Brexit threatens life on the Irish border: in pictures Farmer Gordon Crockett’s Coshquin farm straddles both Derry/Londonderry in the North and Donegal in the Republic. ‘At the minute there is no real problem, you can cross the border as free as you want. We could cross it six or eight times a day,’ said Crockett. ‘If there was any sort of obstruction it would slow down our work every day’ Reuters Brexit threatens life on the Irish border: in pictures John Murphy flies the European flag outside his home near the border village of Forkhill, Co Armagh Reuters Brexit threatens life on the Irish border: in pictures Potter Brenda McGinn stands outside her Mullan, Co Monaghan, studio – the former Jas Boylan shoe factory which was the main employer in the area until it shut down due to the Troubles. ‘When I came back, this would have been somewhere you would have driven through and have been quite sad. It was a decrepit looking village,’ said McGinn, whose Busy Bee Ceramics is one of a handful of enterprises restoring life to the community. ‘Now this is a revitalised, old hidden village’ Reuters Brexit threatens life on the Irish border: in pictures Union Flag colours painted on kerbstones and bus-stops along the border village of Newbuildings, Co Derry/Londonderry Reuters Brexit threatens life on the Irish border: in pictures Grass reflected in Lattone Lough, which is split by the border between Cavan and Fermanagh, seen from near Ballinacor, Northern Ireland Reuters Brexit threatens life on the Irish border: in pictures Donegalman David McClintock sits in the Border Cafe in the village of Muff, which straddles Donegal and Derry/Londonderry Reuters Brexit threatens life on the Irish border: in pictures An old Irish phone box stands alongside a bus stop in the border town of Glaslough, Co Monaghan Reuters Brexit threatens life on the Irish border: in pictures Billboards are viewed from inside a disused customs hut in Carrickcarnon, Co Down, on the border with Co Louth in the Republic Reuters Brexit threatens life on the Irish border: in pictures Seamus McQuaid takes packages that locals on the Irish side of the border have delivered to his business, McQuaid Auto-Parts, to save money on postal fees, near the Co Fermanagh village of Newtownbutler. ‘I live in the south but the business is in the North,’ said McQaid. "I wholesale into the Republic of Ireland so if there’s duty, I’ll have to set up a company 200 yards up the road to sell to my customers. I’ll have to bring the same product in through Dublin instead of Belfast’ Reuters Brexit threatens life on the Irish border: in pictures A disused Great Northern Railway line and station that was for customs and excise on the border town of Glenfarne, Co Leitrim Reuters Brexit threatens life on the Irish border: in pictures Alice Mullen, from Monaghan in the Republic of Ireland, does her shopping at a former customs post on the border in Middletown, Co Armagh. ‘I’d be very worried if it was a hard border, I remember when people were divided. I would be very afraid of the threat to the peace process, it was a dreadful time to live through. Even to go to mass on a Sunday, you’d have to go through checkpoints. It is terribly stressful,’ said Mullen. ‘All those barricades and boundaries were pulled down. I see it as a huge big exercise of trust and I do believe everyone breathed a sigh of relief’ Reuters Brexit threatens life on the Irish border: in pictures A bus stop and red post box stand in the border town of Jonesborough, Co Armagh Reuters

The Independent reported earlier this week that Commission officials were completely opposed to any time-limiting of the backstop. They say commitments already made by British negotiators in December – that the backstop would apply “unless and until” another solution is found – rule out a time-limit.

The UK’s transition is designed to give officials more time to come up with another solution to solve the border – but means there would be yet another cliff-edge.