Boris Johnson has taken his first step towards breaking a treaty – but the Lords may still stop him

Anyone who thought the rolling Brexit constitutional crisis was brought to an end by the election in December may have to think again

Ed Miliband briefly became the successful leader of the opposition he never was against David Cameron. Having held the job for five years, he knows something about how to make a parliamentary speech, and it must be liberating to do so without the burden of leadership prompting caution in every phrase.  

Boris Johnson tried to look as if he was contemptuous of sixth-form debating nonsense, but succeeded only in looking sheepish as Miliband mocked his ministers’ ever-changing attempts to explain why he wanted to repudiate a treaty he had only just signed.  

Miliband, the shadow business secretary, was standing in for Keir Starmer, who was isolating at home because one of his family is waiting for a coronavirus test result. But the former Labour leader’s speech was the entertaining sideshow, not the main event. The serious points were all being made within the Conservative Party, rather than across the floor of the Commons.  

Johnson was subdued as he tried to persuade the doubters on his side that the clauses in the bill were a mere insurance policy that he had no intention of using; it was just that a responsible government had to plan for the worst, he told them.  

What was striking was that at no point did he admit that the proposed legislation would break international law – the blunt admission with which Brandon Lewis, the Northern Ireland secretary, set off the chain of explosions of the past week. 

The prime minister said soothingly that, “of course, it is the case that the passing of this bill does not constitute the exercise of these powers”, and reassured MPs that, in the unlikely event that he ever felt he did have to tear up an international treaty, there would be a further vote in parliament before it happened.  

Some possible rebels seemed placated. Steve Brine, a former minister who had the Tory whip removed by Johnson last year, asked for an assurance that the government was still trying to secure a trade deal with the EU. The prime minister was happy to oblige.  

But Sir Robert Neill, the Conservative backbencher who is leading the revolt, made it clear that he was having none of it. He made the same point as a string of Tory rebels: that if the EU had indeed threatened to try to charge tariffs on goods passing between Northern Ireland and the rest of the UK, as Johnson claimed, the UK’s first resort should be to use the arbitration procedure set out in the withdrawal agreement.  

However, the number of Tory rebels was insufficient to threaten the progress of the bill through the Commons. Several MPs who abstained might vote against the government when it comes to a series of amendments next week, but it doesn’t look as if there will be nearly enough to overturn the government’s majority of 78, especially as it is bolstered – on this issue – by the Democratic Unionist Party’s eight MPs.  

The crunch point for this bill will come in the House of Lords, where the Conservatives have no majority and where even Brexiteer Tory peers such as Lord Howard and Lord Lamont think that repudiating treaties is a terrible idea. 

If the Lords did vote to obstruct the Commons it would be another historic clash. Anyone who thought the rolling Brexit constitutional crisis was brought to an end by the election in December may have to think again.