David Cameron has become the fifth former prime minister to criticise Boris Johnson’s international law-breaking Brexit plan.
The former Tory premier has said he has “misgivings” over his successor’s internal market bill, which is due to be debated in the Commons today.
The bill unpicks parts of the Withdrawal Agreement (WA) negotiated last year to give UK ministers key powers to decide when EU rules apply to Northern Ireland.
Johnson faces a major rebellion from Tory backbenchers over the bill.
Tory former prime minister David Cameron said: “Passing an act of parliament and then going on to break an international treaty obligation is the very, very last thing you should contemplate.
“It should be an absolute final resort.
“So, I do have misgivings about what’s being proposed.”
He added: “And, of course, the bigger picture here is that we are in a vital negotiation with the European Union to get a deal and I think we have to keep that context, that big prize in mind.
“And that’s why I have perhaps held back from saying more up to now.”
It follows a joint piece by John Major and Tony Blair in the Sunday Times urging MPs to reject the legislation.
Last week, Theresa May also shared her concerns about the prospect of the UK breaking an international agreement and Gordon Brown has also spoken out.
Justice secretary Robert Buckland on Sunday suggested he may resign over the plan.
Former attorney general Geoffrey Cox, a prominent Brexiteer, has also hit out at Johnson’s approach, writing in the Times: “It is unconscionable that this country, justly famous for its regard for the rule of law around the world, should act in such a way.”
The government meanwhile claims the bill protects the Good Friday Agreement, which secured peace in Northern Ireland.