Rishi Sunak is set to push his revamped Northern Ireland protocol through the Commons despite hardline Conservative Brexiters rejecting the plan as an unacceptable failure that does not deliver any of its stated claims. The verdict of the European Research Group (ERG), which followed a similar rejection by the Democratic Unionist party on Monday, means Sunak is likely to face a Tory rebellion over the revised post-Brexit trade arrangements in Northern Ireland on Wednesday, although it appears unlikely to be significant. While still influential, the ERG is a notably diminished force from the period of Brexit votes under Theresa May’s prime ministership, when it would boast of having close to 80 members ready to defy the government en masse. Announcing the decision of the ERG’s “star chamber” of legal advisers on Tuesday, the group’s chair, Mark Francois, castigated the plan but declined to confirm he would vote against it. The ERG would not instruct members what to do, he told reporters following a meeting of members that appeared to be thinly attended, with some reports saying fewer than 20 MPs had appeared. The ERG does not give information on its membership, but Conservative MPs estimated a rebellion would be likely to see fewer than 20 oppose the plan or abstain. Asked how many Tories would actively vote against the government, one MP predicted: “I wouldn’t be surprised if it was only four or five.” Wednesday’s vote is not to approve the entire plan, unveiled last month by Sunak after talks with Ursula von der Leyen, the European Commission president. This introduces a “green lane” for the bulk of goods between Northern Ireland and the rest of the UK, as well as what is billed by ministers as an effective veto on new EU regulations for the devolved Stormont assembly. The decision for MPs is simply whether or not to approve a statutory instrument, a form of secondary legislation, to implement the veto element, known as the Stormont brake. Quizzed by MPs about why there had not been more time to scrutinise the entire deal, Chris Heaton-Harris, the Northern Ireland secretary, said it was important to get the brake mechanism in place “sooner rather than later”. Asked by the European scrutiny committee what other Commons votes there would be, Heaton-Harris was opaque, saying only: “There are going to be future opportunities. And parliament will always find a way, if the government doesn’t allow it, to have its say.” The ERG’s 52-page report on Sunak’s deal essentially rejected every aspect of what is formally known as the Windsor framework. Francois told reporters that Sunak’s plan would leave EU law “supreme”, adding: “The green lane is not really a green lane at all, the Stormont brake is practically useless, and the framework itself has no exit, other than through a highly complex legal process.” He strongly indicated the group would recommend voting against the proposal, but said a final decision would be made at another meeting before the debate. Heaton-Harris, however, told the committee it was untenable to have the current situation in which the DUP’s unhappiness with the existing protocol, negotiated by Boris Johnson, meant the party was boycotting the devolved assembly, which has not sat for over a year. “You can ignore it for a certain period of time,” he said. “But it was obvious it was not functioning because of the way the current protocol is working in Northern Ireland.” A potentially bigger headache for Sunak and Heaton-Harris is whether the DUP will return to the assembly and the power-sharing Northern Ireland government if the revised plan comes into force. A leading DUP MP, Sammy Wilson, said on Tuesday that his party would “continue the fight” against the plan, also indicating that it could continue its boycott of the Northern Ireland assembly at Stormont. Speaking on BBC’s Good Morning Ulster on Tuesday, Wilson, the DUP’s Brexit spokesperson, was asked by Colum Eastwood, the leader of the moderate nationalist SDLP, when the DUP could return to Stormont. Wilson replied: “Colum, you may be prepared to roll over, to having powers taken away from the people who are elected to Stormont, we’re not.”