I am pleased to say that I seriously underestimated Rory Stewart. Though I have long admired his grasp of policy, compassionate beliefs and rich hinterland of experience, I thought that, up against it in the toe-to-toe combat of a leadership contest, he might turn out to have a glass jaw.

How, I wondered, would this rangily eccentric figure, a learned but vulnerable character from the pages of A Dance to the Music of Time, fare against the Flashman-style bully boys of Brexit. And the answer is: pretty damn well. The International Development Secretary has turned out to be the Rocky Balboa of this battle, the rank outsider who has taken everything his rivals have thrown at him, and continued to throw his own punches.

Like all good ideas, Stewart’s has been, at its core, astonishingly simple: he wanders around the country telling people the truth. And, in a contest in which the frontrunner’s signature philosophy is a belief that you can “have your cake and eat it”, this is a seriously radical strategy.

Stewart stands unashamedly and boldly for cake-decisiveness: when it comes to baked goods, a statesman is obliged to select consumption or retention. Of course, in any mature leadership contest, especially one whose victor will become prime minister, this approach ought not to be contrarian. To govern, after all, is to choose.

Essentially, what the occupant of Number 10 does — or should do — all day is observe a figurative conveyor belt of cakes, saying: “Have… eat… have… eat… have… have… eat… eat.” But in this post-truth era of meaningless pledges, applause-line rhetoric and politics as entertainment, it is an act of courage to point this out.

Stewart was even candid enough to say that his performance in last night’s BBC candidates’ debate was unsatisfactory. He had, he confessed to Newsnight’s Nick Watt, felt ill at ease in this “strange format of alternative reality”, removing his tie and fidgeting as his Cabinet colleagues shouted at one another.

As Stewart squirmed and stretched, Boris Johnson maintained the ill-tempered countenance of a hungry Buddha whose dinner plans had been disrupted by lesser beings. He conspicuously evaded sharp questions from the BBC’s moderator, Emily Maitlis — “Can you hear me, Mr Johnson?” He refused to be pinned down on his proposal to cut taxes for higher earners, his position on Heathrow’s third runway, and (most shamefully) his part, as foreign secretary, in the extended incarceration in Iran of Nazanin Zaghari-Ratcliffe. “Words have consequences,” said Maitlis. Too right.

Stewart is not going to be the Conservative leader — not this time, anyway — and he knows it. Maddened by Brexit, longing for the candy rush of pseudo-Churchillian confidence, mysteriously persuaded that its problems can be solved by brio and bombast, the party has more or less made its collective mind up that Theresa May’s successor will be Johnson. One can take nothing for granted with this calamity-prone politician. But the race is self-evidently his to lose.

In this context, most of the contenders have been positioning themselves as future members of a Johnson government: pitching for the jobs that they have a chance of getting, rather than the one that they are notionally pursuing. All except Stewart, that is.

His explicit refusal to serve under the presumed victor marks him out. But as what?

"In this wretched race Stewart has emerged as the voice of reason: revolutionary in these Trumpian times"

I think Stewart’s plan is to act as the conscience of the Conservative Party. Not, I suspect, in a priggish or clunkily-woke way: as the Left loses no time in reminding us, he is a Conservative and has voted for many tough Conservative measures in his time.

Instead, Stewart stands for inconvenient truths, a constant champion of politics as the art of the possible, not a branch of showbusiness. As the other candidates promised spending pledges and tax cuts as though the hard-fought years of fiscal conservatism and deficit reduction had been no more than a phase, Stewart reminded them that they, like Jeremy Corbyn, had yet to supply the GPS co-ordinates of the magic money tree.

“I’m going to be straight with people,” he said. “I don’t think this is the time to be cutting taxes. I’m not thinking about the next 15 days, I’m thinking about the next 15 years.” The other four didn’t like that adult intervention one bit.

Worse, Stewart refuses to swoon at the shrine of direct democracy, stubbornly defending the representative variety against its assailants. It is deeply alarming that Johnson has reportedly declined, in private, to rule out suspending Parliament if such a measure is necessary to force through Brexit by October 31.

Stewart is right to resist all such measures with every fibre of his being and to insist that — whatever his colleagues may wish to the contrary — Britain cannot, in practice, leave the European Union without the affirmation of the Commons.

It is extraordinary that a fundamental constitutional norm of this sort should have to be spelt out and defended in a Conservative leadership contest. But it does. It is breathtaking that senior Tories should need to be told that their fiscal sums have to add up as well as their polling numbers. But they do.

In this wretched race, Stewart has emerged as the voice of reason and practicality: a revolutionary position to adopt in these Trumpian times. He is not going to be the next prime minister, but we are going to be hearing a lot more from him.

That, if nothing else, should be a cause for optimism.