Theresa May's compromise Chequers deal looked to be in jeopardy last night after Downing Street accepted four amendments to its customs bill put forward by Brexiteer Tories.
One of the amendments forces the British government to commit itself in law not to allow a customs border down the Irish Sea – a move that potentially rules out the EU's 'backstop' on customs.
A second amendment could stop the UK from collecting tariffs for the EU, a key part of cabinet agreement thrashed out at Chequers earlier this month.
Faced with the possibility of revolt by Brexiteers at Westminster last night, Mrs May bowed to pressure and accepted crucial changes to her plans for leaving the EU.
DUP MP Sir Jeffrey Donaldson welcomed the amendment vetoing a border in the Irish Sea.
"We are pleased the government has accepted this amendment to the customs bill as we felt it was important to have the clearly stated objectives of the government outlined in the white paper, enshrined in law so that any future customs arrangements are informed by that law," he told The Irish News.
"Clearly the amendment states that there can be no customs agreement that puts a border in the Irish Sea."
He said it was "good news for Northern Ireland business".
"It means we will continue to be unfettered access to the UK market, which is our biggest and most important market in terms of generating income," he said.
Sir Jeffrey said the prospects of agreeing a deal with the EU were still good.
"We believe the amendment is entirely consistent with what was agreed in December – we want a soft border with the Irish Republic but also have unfettered access to the UK single market," he said.
"We hope that a free trade agreement can be agreed between the UK and the EU that will allow for that soft border option and will enable Northern Ireland to continue to trade with the Republic of Ireland and the rest of the EU in the context of a new trading arrangment."
At Westminster, a Brexiteer source told the Press Association the amendments put forward by Eurosceptics such as Jacob Rees-Mogg, Sir Bernard Jenkin, Priti Patel and Iain Duncan Smith, confirmed that "Chequers is dead on arrival".
Tory Remainer Anna Soubry suggested Mr Rees-Mogg was now "running Britain", while Labour MP Stephen Kinnock accused Mrs May of "dancing to the tune" of the European Research Group (ERG) of Tory Brexiteers.
But Mrs May insisted the amendments do not change the blueprint agreed at her country residence.
"I would not have gone through all the work that I did to ensure that we reached that agreement only to see it changed in some way through these Bills," she told MPs.
"They do not change that Chequers agreement and the minister from the despatch box later today will be making that clear."
Downing Street insisted the amendments it had accepted were still consistent with the plans in the Chequers agreement but the move may limit the government's room for manoeuvre in exit talks with the EU.
"We will be accepting these four amendments because we feel they are consistent with the white paper we published last week," a source told the Press Association.
Peter Bone, a signatory to the amendments, said the whole situation was a "shambles" and called for the Chequers plan to be taken off the table.
"I can't possibly dress it up in any other words than it's an absolute shambles and a self-inflicted shambles by Number 10," he said.
The other amendments require the UK to have a separate VAT regime from the EU and force the prime minister to table primary legislation if she wishes to keep Britain in the customs union.
But Mrs May faces further danger today with pro-EU Tories tabling amendments to the Trade Bill, which returns to the Commons.
