There’s one question that could scupper Boris Johnson’s campaign – which is why he’s ducking the debate

How does he plan to leave without a deal when parliament will stop him?

Why is Boris Johnson hiding from journalists? He won’t take part in the Channel 4 debate on Sunday. He can’t fit in the hustings in front of Westminster journalists on Monday because, he says, he has to prepare for the next hustings in front of Conservative MPs that afternoon.

He can’t find space in his diary for a big public event until the BBC’s TV debate on Tuesday night – coincidentally after the second ballot of Tory MPs, in which he will probably have consolidated his position as the frontrunner.

His handlers were so worried by the idea that Johnson is “frit” that they arranged an 18-minute recorded interview with Mark Mardell for BBC Radio 4’s World At One on Friday. BBC sources say they were given ten minutes notice of the candidate’s arrival; the Johnson campaign say it was 30 minutes.

Either way, it was an attempt to make the prime minister presumptive available for sustained questions while keeping him on as short a leash as possible.

Johnson is trying to strike a balance. On the one hand, he knows the frontrunner has most to lose from exposure. That was why leaders, from Margaret Thatcher to John Major to Tony Blair, found ways of scuppering TV debates in general elections without ever appearing to say no.

The debates happened in 2010 only because David Cameron, having challenged Gordon Brown when Brown became prime minister, was then trapped when their roles were reversed and Brown was the underdog. Then came Theresa May’s disastrous campaign in 2017, when her hiding from public scrutiny became one of the big stories of the election.

This upended the conventional wisdom that it was in the frontrunner’s interest to avoid scrutiny. The prime minister’s refusal to take part in debates or to meet members of the public was one of the criticisms of her that cut through to the voters.

Johnson could see that the idea that he was dodging scrutiny was becoming a big theme of the coverage of this campaign. His temptation, I am told, was to dismiss it as an obsession of journalists who like nothing better than talking about themselves, but he was persuaded he needed to do something about it. Hence the Mardell interview.

In fact, Johnson had a point. It is a weakness of the coverage of any election that it can be diverted into questions of process: who is backing whom; who is interviewing whom; will there be TV debates; if so, what should their format be?

These are all interesting, but the story ought not to be that Johnson is trying to avoid being asked hard questions; instead it ought to be: what question does Johnson not want to be asked?

I think it is this: How will he take us out of the EU on 31 October “deal or no deal”? He knows that parliament will not allow the UK to leave with no deal. His supporters were gleeful this week when Jeremy Corbyn failed to take control of the Commons timetable, saying this showed that the opponents of a no-deal Brexit did not have the votes they needed to block it.

But Wednesday’s vote, which Corbyn lost by a margin of 11, was just an opening shot. We saw on 3 April that, when the Commons finds itself close to the brink of a no-deal exit, it will vote against it. Then, parliament passed a law requiring the prime minister to seek an extension of EU membership rather than allow the UK to leave without agreement nine days later.

That act was passed by just one vote – but it would have been more if Theresa May had not already said she would ask for an extension.

So Johnson knows that parliament will vote to force him to ask for an extension when it is up against the deadline. This week, not enough MPs were persuaded by Oliver Letwin’s argument that they had to act now to be sure of blocking a no-deal exit.

Those doubtful MPs are right. John Bercow, the speaker, has made it clear that ways will be found to allow the majority of the Commons to assert itself. Regardless of his personal views on Brexit, he is right to say so. No prime minister should try to take the UK out of the EU on terms opposed by the House of Commons.

It may not need this week’s device of using an opposition day debate. It probably will not need Rory Stewart’s suggestion that a suspended Commons should convene itself in Methodist Central Hall on the other side of Parliament Square.

Bercow has hinted that MPs could use an application for an emergency debate to legislate against the government. Johnson knows parliament could use this device to pass an act to prevent it being suspended, and another to stop a no-deal exit.

So, if the new prime minister cannot get a revised Brexit deal through parliament, how can Johnson guarantee that we will leave the EU with or without a deal?