Simon Case, the Cabinet Secretary, stood outside the committee room staring thoughtfully at a large oil painting of Denis Healey. It’s a striking image, the more so because it’s largely rendered in different shades of brown, against a dark background.

Case was the latest witness to appear before the Public Administration Committee, which is chaired by boy-inquisitor William Wragg, a Tory who, at the age of 34, manages to seem at once 12 years old and not a day under 60.

The official subject of the hearing was something to do with Greensill, the company that employed David Cameron and got into a huge amount of trouble (these may or may not be related). But the real subject of all Wragg’s hearings is the moral black hole that is 10 Downing Street these days. Witnesses are brought in to try to describe the things they’ve seen there, but it’s clear that gazing into the abyss has cost most of them their sanity. The last chap they had before them, Lord Geidt, resigned the next day and moved to a Scottish island to farm sheep.

Was Case made of sterner stuff? Like Wragg, he seems very young in the role. There wasn’t a grey hair in sight. His beard — who was the last Cabinet Secretary to have a beard? — was neatly trimmed.

The chairman put it to Case that “propriety and ethics” — Mandarin-speak for doing the right thing and not doing the wrong thing — were the most difficult aspects of his job. There was a long pause. “Definitely,” Case replied, with some feeling. He explained it was his duty both to “to support the government of the day” and to be “upholding values”. Sometimes, he noted, these two simultaneous duties created “challenges and conflict”. The committee managed to contain its astonishment.

“The government of the day is one which is not remotely afraid of controversial policies,” Case, who was working for the Royal Family that time that the prime minister lied to the Queen, noted, with gentle understatement. “It believes it has a mandate to test established boundaries.”

It was a fascinating insight into Downing Street life. Did you realise that a vote for Brexit was a vote for Boris Johnson to have a £150,000 treehouse? Are you confused that the 2019 election gave the prime minister a mandate both to sign his Brexit deal and to rip it up? That, it turns out, is what Johnson believes.

And this, Case was telling us, is what he’s wrestling with. Here is a man whose career, including and perhaps especially the vague bits around the time he was doing his PhD in the work of the intelligence services, has been devoted to the service of his country, and now that country has a sex-crazed gorilla at the controls and it is his job to keep the show on the road as best he can (I paraphrase). John McDonnell stared at him, fascinated.

Wragg seemed to be looking at Case over the top of his glasses, an effect particularly impressive as he doesn’t wear them. How much of Case’s workload, he wanted to know, was taken up with questions of ethics.

Sustained periods with Johnson will break a man’s spirit

“It varies,” the civil servant replied, before conceding that at moments it was as much as a third of his time. Keep in mind that his time in the job has seen a pandemic, war in Europe and raging inflation. But also, he didn’t quite say, keep in mind that the prime minister is Boris Johnson. In that context, spending 15 or 20 hours a week disentangling ethical knots looks like pretty good time management. It wasn’t, he reminded us, simply stuff around cash for wallpaper and jobs for Carrie. There were “issues where policy ambition raises questions around ethics and legality”. I’ll bet there are. Under the desk his right foot tapped furiously away at the base of his chair. I’d assumed these chaps were trained to withstand waterboarding, but sustained periods with Johnson will break a man’s spirit.

We moved to the resignation of Lord Geidt, until so recently the prime ministerial ethics adviser. “There certainly is a lot more pressure on these roles than there used to be,” Case said, without getting into the question about why that should be. His foot was tapping at 180 beats per minute. Geidt, he observed sadly, “had all the required experience” to do the job.

But did he? Does anyone? McDonnell grilled Case on the jobs-for-Carrie question, to which Case explained that it was up to the prime minister whether the prime minister should be investigated. McDonnell wanted to know if he’d discussed it with Johnson. Case refused to answer.

“Have you any responsibility as one of the most senior civil servants in government to uphold standards?” McDonnell asked.

“I’m very aware of my responsibilities,” Case replied with some heat, “and I take them very seriously.”

That was his evidence in a nutshell. He’s out there every day, just trying to keep the ship afloat, wrestling with a duty to provide honest, lawful government under the command of a man without the slightest interest in either. He knows by now that the portraits of him will also be painted in shades of brown against a murky background. It’s a filthy job, but someone has to do it.