Rishi Sunak’s effort to push his Northern Ireland Brexit plan through parliament is descending into acrimony after a minister said Boris Johnson risked being seen as “a pound-shop Nigel Farage” for voting against the plan. Steve Baker, a Northern Ireland minister who was formerly a leading backbench Conservative Brexiter, made the remark after both Johnson and Liz Truss said they would oppose the proposal in the Commons on Wednesday. Johnson has in particular urged a notably robust line against the EU, saying the prime minister should scrap his deal and instead push ahead with a law that would allow the UK to unilaterally change the Northern Ireland protocol he negotiated, a course of action likely to cause a trade war with Brussels. “He’s got a choice,” Baker told Sky News when asked about Johnson’s decision. “He can be remembered for great acts of statecraft that he achieved or he can risk looking like a pound-shop Nigel Farage. And I hope he chooses to be remembered as a statesman.” Downing Street had been sanguine about the potential scale of a Conservative rebellion against the plan, even with the opposition of the European Research Group (ERG) of Brexit-supporting Tory MPs, as well as the Democratic Unionist party. But the intervention on Wednesday of the two previous prime ministers, with the former home secretary Priti Patel also saying she would oppose the plan, could swell the number of opponents, potentially leaving Sunak requiring Labour votes for it to pass. The vote is only on one aspect of Sunak’s revised deal for post-Brexit trade arrangements in Northern Ireland, sealed last month, the so-called Stormont brake to veto new EU regulations. However, it is seen as default vote on the entire plan. Johnson said: “The proposed arrangements would mean either that Northern Ireland remained captured by the EU legal order – and was increasingly divergent from the rest of the UK – or they would mean that the whole of the UK was unable properly to diverge and take advantage of Brexit. “That is not acceptable. I will be voting against the proposed arrangements today. Instead, the best course of action is to proceed with the Northern Ireland protocol bill, and make sure that we take back control.” A source close to Truss said she planned to vote against it too. Truss is understood to believe the prime minister’s Windsor pact does not “satisfactorily resolve the issues thrown up by” the Northern Ireland protocol and “almost fatally impinges” on the UK’s ability to diverge from EU rules and regulations. Johnson is expected to briefly leave his questioning at the Commons privileges committee over Partygate on Wednesday afternoon to have his say on the measure. The ERG announced on Tuesday that it did not believe Sunak’s revised plan met the stated objectives of the government. Following a second meeting on Wednesday, the ERG confirmed it would recommend voting against the plan. Mark Francois, the ERG’s chair, told reporters he had “recommended to the group that we should vote against”. The ERG does not release details of its membership, but some reports said up to 30 MPs were at the meeting. DUP officers met on Monday and took a unanimous decision to reject Sunak’s revised plan for post-Brexit trade arrangements in Northern Ireland, the party’s leader, Sir Jeffrey Donaldson, said in a statement. “It does not deal with some of the fundamental problems at the heart of our current difficulties. There remain key areas of concern which require further clarification, reworking and change as well as seeing further legal text,” Donaldson said. The Conservative backbencher Peter Bone is among Tories who have signalled they may join Johnson and vote against the deal. He said he was “pretty miffed” about the government’s approach to a vote on the Stormont brake. The former Commons deputy leader told Sky News: “We were promised a full debate on the Windsor framework. If I get a question at PMQs I’m going to ask the prime minister what happened to our wider vote. “So I’m really pretty miffed that the government is avoiding scrutiny on this and on the brake itself it seems to fail all the tests. “If that is the case, I’m going to listen to the debate. I’m going to go to meetings this morning, but if I had to vote at this moment in time, I should vote against.”