Tuesday night, and I am compelling myself, with some effort, to watch the television debate between Boris Johnson and Jeremy Corbyn. It’s an excruciating format at the best of times; and this, let’s face it, is not the best of times in British politics.

If the debate hardly makes for satisfying television, though, it nonetheless produces some interesting moments, for those seeking straws in the electoral wind.

That neither leader knows which day of the week it is when it comes to the politics of the Union comes as no surprise; asked whether the Union matters more than Brexit, Johnson says “yes” without showing any willingness to compromise with Scotland’s wishes on any matter, and Corbyn does not answer the question at all.

Boris Johnson and Jeremy Corbyn provided some less than compelling television in the ITV Leaders Debate (Picture: Jonathan Hordle//ITV via Getty Images)

Nor is it surprising that Corbyn outclasses Johnson on issues around investment in public services, and the improvement of wages and benefits; he and John McDonnell have been working on these policies since he became leader four years ago, whereas the Tories’ sudden conversion to high public spending, and to ending austerity, is very recent indeed.

Nicola Sturgeon under fire over private firms doing 'routine operations' in NHS ...

What’s more interesting, though, is that just as he cannot get his head round the Scottish constitutional question, so Corbyn cannot get to grips with the details of Brexit.

From the outset of the debate, which begins with the Brexit issue, Johnson talks his usual gold-plated nonsense about how his wonderful Withdrawal Agreement will “Get Brexit Done”, and open the way to a brilliant future. There are two clear answers to this.

Johnson’s dreadful deal

The first is the familiar argument that no withdrawal agreement will “get Brexit done”, but will only mark the beginning of a protracted and agonising trade negotiation with the EU 27.

The second, though, is that Johnson’s Withdrawal Agreement is a dreadful deal for the people of Britain; one that, even for Brexiteers, absolutely should be renegotiated, as Labour policy suggests.

For all the Prime Minister’s mendacious denials, it clearly places a regulatory border down the Irish Sea. It also takes Scotland, England and Wales out of the single market to which we desperately need access, abandons a whole swathe of EU-guaranteed employment rights, and opens the way for a serious deterioration in environmental protection and food standards.

And the fact that Corbyn apparently cannot say this – in three or four brief bullet-points that would effectively destroy Johnson’s core argument that passing this deal is somehow a positive prospect – is his greatest weakness in this election.

The debate’s single most revealing moment, though, came when the two men were invited to respond off-the-cuff to questions about integrity and trust in public life, and about this week’s crisis in the royal family following Prince Andrew’s disastrous attempt, via a BBC television interview, to respond to serious accusations arising from his friendship with the convicted paedophile Jeffrey Epstein.

For Corbyn, the politics of gender is part of his home territory, as a lifelong campaigner on the left. His immediate response to the question on Prince Andrew was therefore to express concern for Epstein’s victims and their need for justice; and when he was asked to say in a couple of words how he felt the monarchy was doing at the moment, he replied wryly, “needs some improvement”, a response that more or less perfectly reflected the public sense that all is not well, but that this is perhaps not the moment for an all-out assault on a respected 93-year-old monarch experiencing yet another “annus horribilis”.

Oxford Union face

Johnson, though, seemed almost comically out of his depth with this area of questioning. Not only did he completely evade the questions on trust in politics – at the very moment when the Tory Twitter feed was being rebranded as “Fact Check UK” – but he seemed utterly out of his depth on the matter of Prince Andrew and the treatment of women, assuming his “witty” Oxford Union face, and blustering that “the institution of the monarchy is beyond reproach”.

For Johnson and his mates, the cleverly nuanced emphasis would be on the idea of the “institution”, as opposed to some of its current members. What most people will hear, though, is the phrase “beyond reproach”, with its echoes of “above criticism”; that is, about as disastrous an expression of uncritical faith as any politician could have made, at such a moment, and hopelessly out of step with public feeling.

So this is where we stand, at this moment in British politics. At the height of Britain’s greatest constitutional crisis in a century, we have an opposition leader so uninterested in constitutional detail that he cannot coherently savage the deeply flawed EU withdrawal deal Johnson is trying to foist on the nation.

And at a key moment of cultural change in gender politics, when long-established patterns of power and abuse are being challenged, we have a Prime Minister who lacks the language even to say the right thing on these issues, far less do it; and whose chaotic private life suggests an attitude to women – and to fatherhood – that is unreconstructed at best.

Johnson is emerging from this campaign so far, in other words, as a populist without the common touch, and a would-be demagogue who struggles, under pressure, to speak the language of the people, rather than of the political and media establishment he has been amusing for so long.

Although he and his supporters mimic so many of Donald Trump’s strategies and attitudes, he visibly lacks Trump’s visceral far-right convictions, which help hold together his key alliance between the wealthy and privileged on one hand, and the angry working poor on the other.

And Johnson’s shallowness, as a politician, means that despite the massive strategic and polling advantage with which he enters this campaign, there is still everything to play for between now and 12 December. For all Corbyn’s weaknesses, the possibility remains that another three relentless weeks of campaigning may increasingly expose Johnson’s lack of real political conviction; and demonstrate that when it comes to the nitty-gritty of politics, to be deadly serious about your own career – while treating everything else as a bit of a joke – is finally to be not quite serious enough.

General election: Why Boris Johnson’s political career may not survive next three weeks – Joyce McMillan