“It’s been an especially busy year,” Lord Geidt, ethics adviser to the prime minister, sighed. He was giving evidence to Parliament’s Public Administration Committee. For some reason — and we never really got to the bottom of why — people keep writing to Geidt complaining about things.

Geidt really shouldn’t be very busy at all, because his main job is to offer Boris Johnson his thoughts about the difference between right and wrong, and Johnson very obviously doesn’t want to hear them.

It was, to Geidt, a great mystery

Older readers may remember that the previous holder of the job, Sir Alex Allan, resigned after Johnson refused to accept his findings over Priti Patel’s bullying of her staff. There was then a long period while Number 10 hunted for someone willing to take on the job of trying to persuade the prime minister to behave in a recognisably ethical manner. Geidt, a former secretary to the Queen, eventually agreed. He explained to the committee that it was important someone do the job because otherwise the public would lose confidence in the system.

The Committee was trying to understand why the public had the impression that the government was utterly rotten. It was, to Geidt, a great mystery. The Ministerial Code on behaviour, he said several times, was fine. The Nolan Principles of Public Life were still in there, undiluted. “I do think the present arrangements are workable and capable of being satisfactory,” he mused. And yet, somehow, there remains an impression that there is an ethical vacuum at the heart of government. Perhaps the code is printed in the wrong font.

Was it possible, someone asked, that the problem was that time when the prime minister broke the law?

“Many people have written to me making this point,” Geidt said, with an air of surprise in his voice. He tried to see it from others’ point of view. “It’s reasonable to say that perhaps a fixed penalty notice and a prime minister paying for it may have constituted not meeting the overarching duty under the code of the prime minister not complying with the law,” he said, as though it were an entirely theoretical question, like the one about how many press office staff can fit on the Number 10 swing. But people didn’t need to worry, he explained, because the prime minister had made a statement saying he hadn’t broken the code, and that was an end to the matter.

Geidt’s position seemed to be that any prime minister, upon realising they had breached the ministerial code, would immediately tender their resignation to the Queen. As Johnson hasn’t resigned, he can’t have broken the rules. The prime minister’s unstoppable force had met Geidt’s highly moveable object.

He has to work with the tool that he’s got

Why, Ronnie Cowan wanted to know, didn’t Geidt offer the prime minister advice about following the code? “If the prime minister were to decline that advice,” the adviser explained, “we would find ourselves in a position where self-evidently the confidence would have been lost between the prime minister and the adviser.”

There we had it. Geidt, it is clear, believes that it is vital for the maintenance of public trust in government that he keep going to work. He cannot keep going to work if his advice is ignored. Clearly Boris Johnson is not going to follow his advice. So he must not give advice. Otherwise the public might lose faith in politics.

His position, we realised, is like one of those puzzles where there are two doors and one guard who always tells the truth and one who never does, except in this case there’s just one prime minister, and he’s obviously lying about everything, and the challenge is not to resign over it.

“Is it possible to perform that role without trust?” asked William Wragg, the chairman. Geidt replied that there had been “signs of some success” in getting Johnson to behave in an honest and straightforward manner, as though Her Majesty’s chief minister was a toddler struggling with potty training.

Geidt said he’d been forced to take on a staff to help him. “The amount of traffic that comes to the office of the independent adviser has grown very greatly in my time.”

“Why do you think that is?” Wragg asked, deadpan.

Had he, as was reported, considered resigning? “Resignation is one of the few tools available to an independent adviser,” he said. “It’s always on the agenda,” he added. One can imagine it must be.

However, it’s clear he’s not going to use it. “It’s right and proper that there should be an independent adviser in post,” he explained. When John McDonnell accused him of overseeing a “whitewash”, Geidt replied “Thank you”, and seemed to mean it. Perhaps he thought it was a compliment.

In the end, his position was summed up by a repeated phrase: “I’m trying my best to work with what I’ve got.” Wragg picked up on it: “Did you mean personalities or the rules?”

“I meant the rules,” Geidt replied.

“I was merely reflecting,” Wragg mused, “on the usefulness of codes and rules if there isn’t a keenness to observe them.” Geidt swerved that one.

At the end, Tory MP David Jones had one last crack. “You have not made any recommendations whatsoever as to how we might improve what you’ve got to work with,” he complained.

Perhaps he hadn’t been listening. Geidt had already explained his view on the matter: he has to work with the tool that he’s got.