Sir Keir Starmer has committed Labour to back Boris Johnson’s new Brexit legislation if the prime minister addresses “substantial cross-party concerns”. The Labour leader accused the prime minister of having “turned the clock back” and of “reigniting old rows” by working to override his own withdrawal agreement. Starmer contended a free trade deal can still be struck with Brussels if negotiators from both sides “hunker down in good faith and break the logjam”. And, writing in the Sunday Telegraph, he threw down the gauntlet to Johnson as he faces a rebellion from within his own party by saying Labour could back the internal market bill. “Labour is prepared to play its part in making that happen. If the government fixes the substantial cross-party concerns that have been raised about the internal market bill, then we are prepared to back it,” Starmer said. “But if they do not, and the talks collapse, then it is their failure and incompetence that will have let the British people down.” But the changes necessary to win Labour’s support are understood to be major, with it needing to no longer risk breaching international law and to address devolved administrations concerns of a “power grab”. Starmer said ministers are facing a task “as ludicrous as it is frustrating” in telling the public to stick to rules to prevent the spread of coronavirus while defending the potential breach of international law. “The priorities of the British people. We should be getting on with defeating this virus, not banging on about Europe,” the MP said. “Get on with Brexit and defeat the virus. That should be the government’s mantra.” Senior Tories are tabling an amendment to the Bill, which is due to be debated in the Commons on Monday. And three Conservative former leaders, including ex-prime ministers Theresa May and Sir John Major, are among those to have called on Johnson to change the legislation. Major and Tony Blair united in the Sunday Times to condemn Johnson’s Brexit legislation as imperilling the Irish peace process, trade negotiations and the UK’s integrity. The Conservative and Labour grandees wrote: “It puts the Good Friday agreement at risk, because it negates the predictability, political stability and legal clarity that are integral to the delicate balance between the north and south of Ireland that is at the core of the peace process. “This has wide-ranging ramifications. It will not only make negotiation with the EU more difficult, but also any trade negotiations with other nations, including the United States. Once trust is undermined, distrust becomes prevalent. “We both opposed Brexit. We both accept it is now happening. But this way of negotiating, with reason cast aside in pursuit of ideology and cavalier bombast posing as serious diplomacy, is irresponsible, wrong in principle and dangerous in practice. “It raises questions that go far beyond the impact on Ireland, the peace process and negotiations for a trade deal – crucial though they are. It questions the very integrity of our nation.”