Hardline Tory Brexiteers have called for a key part of Boris Johnson’s withdrawal agreement to be scrapped, despite voting for it last year.

The European Research Group (ERG) said the Northern Ireland protocol, an attempt to solve the vexed issue of the Irish border and Brexit, “has to go” as unionist politicians claim it has driven a wedge between the region and the rest of the UK.

Responding, Labour said: “The ERG – and this cannot be stressed enough – voted for this.”

The protocol, designed by the EU and UK to avoid a hard border on the island of Ireland, has long proved one of the most troubled parts of Brexit negotiations.

The original version proposed by Theresa May would have seen similar rules applying to the whole UK, but would have restricted the government’s ability to sign free trade deals around the world.

When Johnson took over as prime minister, he ripped up May’s commitment for the whole UK to be treated the same, instead agreeing to move regulatory and customs checks to the Irish Sea, with goods imported into Northern Ireland from Great Britain subject to a range of new processes.

This has caused some disruption to trade since it came into effect on December 31, which could intensify significantly on April 1 when a grace period currently limiting the bureaucracy applied to imported supermarket goods ends.

In a report, the ERG said the EU’s “bungled” and short-lived attempt to suspend the protocol to block vaccines leaving the bloc for the UK via Ireland has created a “political opportunity” for the government to seek to renegotiate this part of Johnson’s deal.

The groups said that although it voted for the protocol as part of Johnson’s withdrawal agreement, “it was not necessarily intended to be permanent” because it can be replaced by a vote in the Northern Ireland assembly.

The group also pointed towards backbench Tory attempts during negotiations to replace the protocol with so-called “alternative arrangements”, which did not make it into the exit deal after being dismissed by the EU.

The UK should now seek to renegotiate the deal and replace it with these alternative arrangements, based on technological solutions, or suspend the protocol and replace it with domestic laws, it said.

ERG chair Mark Francois said: “We will no doubt be told that the EU will never renegotiate the protocol – just as we were repeatedly assured they would never re-open the withdrawal agreement, or indeed abandon the dreaded ‘backstop’, which the protocol eventually replaced when they subsequently did both. 

“Our report explains, in detail, why we believe that the protocol now has to go, or to paraphrase William Hague, why ‘we will not let matters rest there’.”

The Democratic Unionist Party has already demanded the scrapping of the protocol.

Following a meeting of the UK/EU joint committee overseeing the mechanism on Wednesday, Northern Ireland first minister Arlene Foster said the protocol had “completely ruptured the flow of goods from Great Britain to Northern Ireland”.

She called for the UK to take unilateral action, saying Johnson’s should “step up and protect the United Kingdom internal market”.

In a joint statement after the virtual joint committee meeting on Wednesday, Cabinet Office minister Michael Gove and European Commission vice president Maros Sefcovic said both sides committed to the “proper implementation” of the protocol.

Shadow Northern Ireland secretary Louise Haigh said the ERG had voted for Johnson’s Brexit deal, including the Northern Ireland protocol, but now wants to create further instability.

“The ERG – and this cannot be stressed enough – voted for this,” she said.

“This was the deal they demanded, for the Brexit they chose.

“Now they would rather tear things down, and provoke further instability, than show even a hint of responsibility.”