Boris Johnson has made a good start, but he is heading for a fall

Editorial: When MPs return to Westminster on 3 September, the prime minister will be reminded daily that his government is severely constrained

Boris Johnson expects talks with EU on the Irish backstop 'in the coming weeks' and returns Donald Tusk's warning of going down in history as 'Mr No-Deal Brexit' (Getty)

Boris Johnson has had a good start as prime minister, on his own terms, but it is hard to escape the feeling that he is heading for a fall.

He has now been in post for a month, and his boisterous assertion that Britain will definitely be leaving the European Union on or before 31 October has rallied Eurosceptic opinion. The Conservatives are enjoying a modest revival in the opinion polls as former supporters of Nigel Farage’s Brexit Party decide that they like what they hear from 10 Downing Street.

Now for the hard part. So far, Angela Merkel and Emmanuel Macron have been polite, but have offered no real prospect of a withdrawal agreement that is much different from Theresa May’s.

Donald Tusk, the EU president, has been less polite and yesterday he and Mr Johnson engaged in a spat of name-calling, accusing each other of being to blame for a no-deal Brexit if it happens.

And this weekend at the G7 summit in Biarritz Mr Johnson is getting to grips with the realities of talking trade with Donald Trump. As we reported yesterday, it seems that the prime minister is beginning to accept that there are serious obstacles to a free-trade deal with the United States.

The problems are more complicated than the celebrated example of chlorinated chicken. For one thing, any deal has to be haggled line by line through the US congress. It ought to be obvious that the personal friendship between Mr Trump and Mr Johnson is no guarantee of a quick and comprehensive post-Brexit US-UK agreement.

Mr Johnson faces a more fundamental problem, however, which is that he has to get Britain out of the EU first. So far the new prime minister has been able to seize the initiative with windy rhetoric and airy assertions.

But parliament was sitting for only the first full day of his 30 days in the job. When MPs return to Westminster on 3 September, he will be reminded daily that his government, which enjoys with the support of the Democratic Unionist Party a notional majority of just one, is severely constrained.

And on any question relating to Brexit, Mr Johnson’s government is unlikely to be able to muster a majority in the House of Commons at all. That means that, if he cannot find a way through to a revised Brexit deal, he is likely to face a parliamentary block on leaving the EU without agreement.

We are clear what he should do to break that deadlock. He should go back to the people in a new referendum on our relationship with the EU now that the choices are known.

But we recognise that he is unlikely to choose this way out of his approaching difficulties. It seems more likely that the Brexit question will end up going back to the people in a general election – an election in which several parties may be proposing a new referendum on the European question.

One way or another, this is a decision that must return to the people. We must be given the Final Say.