Sir Oliver Letwin ended his speech with a story about an earlier occasion when Britain appeared to be heading for a cliff edge. The Governor of the Bank of England warned that in his view the lenders were about to “go on strike and we would have a meltdown”.

That was just after the general election of 2010, in which no party gained a majority. Letwin later discovered that “the cleverest people in the civil service” had examined whether, if this happened, it would be possible to form a coalition government, and had concluded it would be “absolutely impossible – it could not be done”.

Yet the politicians held talks, and within five days there was a coalition government. What brilliant administrators regarded as a logical impossibility was actually quite straightforward for politicians who accepted the need for compromise.

And he thinks that although the Government should have set out two years ago to discover what form of Brexit could command a majority in the Commons, it is not too late to do so in the next few days, for politicians understand how to accommodate the essential arguments of the other side.

Letwin insisted, as he spoke for his amendment, that he is not proposing “some kind of massive constitutional revolution”. He pointed out that the standing order under which the Government determines Commons business only dates from 1906, so is “not part of our ancient constitution”, and is in any case not applied on Fridays, when Private Members’ Bills are debated.

So Letwin is not, as he put it, a revolutionary. He is actually something much more alarming: an optimist. He believes that with good will and energy, the Brexit problem is soluble.

And he will go on voting for Theresa May’s deal, whether it comes back three times, four times or to infinity, because “I think it’s OK”.

David Lidington, on the front bench, who had opened for the Government, gave a broad smile. Geoffrey Cox, the Attorney General, nodded emphatically. Neither of them looked as if they regarded Letwin as a dangerous revolutionary. They reckoned they could do business with him.

Kenneth Clarke intervened to warn of the danger that in the indicative votes proposed under the Letwin amendment  “we won’t produce a majority for anything”, and said “the single transferable vote is the best way of steering people to one conclusion”.

Letwin reckoned it was important to vote on all the different options which command the support of a substantial body of MPs at the same time, in order to eliminate attempts to game the system.

While Letwin spoke, a spirit of perfect harmony reigned across the Chamber, with Yvette Cooper, Helen Goodman and other Labour members intervening to make constructive points.

And the same spirit of harmony prevailed earlier, at least for most of the time, as Lidington made his opening speech. Only Sir William Cash, and on the Labour benches Kate Hoey, grew exercised about “the lawful authority”, as Cash put it, for the statutory instrument which will change the date on which the country leaves the EU, in order to bring British law into line with European law.

The Speaker, John Bercow, ruled that “EU law trumps UK national law”, a point of which everyone is aware, though he refused to rule off the top of his head on more arcane matters.

But here, one felt, was a glimpse of what the whole argument is actually about. Why should EU law trump UK law? And when will this stop being the case?