When the Prime Minister said she wanted “as little friction as possible”, Jeremy Corbyn inquired, “was she talking about EU trade or the next Cabinet meeting?”

A good first question, to which Theresa May began by declaring: “The Government has a policy…” She was drowned by cries of derision, during which one could not help feeling she looked vulnerable.

When she was able to resume, she said: “…of leaving the EU and obviously as we do so ensuring we have as frictionless trade as possible with the EU.”

May is good at saying where she wants to go, less good at explaining, or deciding, how she intends to get there. Waves beat over the boat while she works out how to steer it.

Corbyn observed there has been no progress for five months, and asked “how much friction she’s willing to accept”.

The Prime Minister repeated that she wants the whole thing done “in as frictionless a way as possible”, and observed that it was “not correct” to say trade was “entirely frictionless” now.

A faint smile played about the thin lips of Corbyn’s adviser, Seamus Milne, who sits in the press gallery for these encounters. One could imagine a close adviser of Robespierre wearing that demeanour as enemies of the people went to the guillotine during the French Revolution.

But Corbyn is not Robespierre. He made a good debating point about the Dutch being “more prepared” for Brexit than we are, because they have taken on extra customs officers and we, apparently, have not.

But after that, the Labour leader reverted to his diffuse style, and asked such long questions that he ceased to be dangerous.

May’s shoulders shook with laughter as he demanded: “Why doesn’t she step aside and let Labour negotiate?”

And the Prime Minister’s head was still attached to her shoulders. Corbyn had once again thrown away the chance to strike a killer blow.

Yet May’s backbenchers cannot have watched this encounter with any pleasure. Corbyn has worked out how to make her look weak.