There’s been a very good reason why Jeremy Corbyn has chosen to avoid Brexit for the past few months at prime minister’s questions. One person with no clear views on Brexit asking another person with no clear views on Brexit to offer some clarity on Brexit is not the most enlightening way to pass 15 minutes of anyone’s time.

It’s still not entirely obvious if the Labour leader has any real clue where he stands on Brexit, but having given a vague hint the previous day that he might be in favour of staying in a customs union, he reckoned he had enough of the moral high ground to finally take on Theresa May over the fault line in her own party. Corbyn began on what should have been safe ground: David Davis’s promise that post-Brexit Britain would be marginally better than a Mad Max dystopia. Couldn’t she raise the bar just a little higher?

May gave no sign of having heard the question, choosing instead to criticise Labour for having no clear Brexit strategy. There were so many possible comebacks to this that Corbyn was spoiled for choice. He could have pointed out that the Tory divisions were far deeper than Labour’s. He could have observed that it was the government’s responsibility to sort out a mess of its own creation. Anything, really.

Instead he said nothing. It was almost as if the whole subject bored him and he was just keen to get on to his next prepared question. Davis had said he didn’t want to lower Britain’s regulatory standards: so why was his department briefing about all the opportunities to be had from deregulation?

“I’ll tell you what we want,” May replied, again failing to answer the question. What she wanted was all the usual stuff. Everyone happy. Everyone better off. People first. Dogs second. And pigs flying.

Corbyn pressed on. In her Lancaster House speech, the prime minister had talked about tariff-free trade; now she was downgrading this to “as tariff-free trade as possible”. Could she explain the difference? May gave it a moment’s thought before deciding that, on balance, she’d rather not. Instead, she’d like to mention all the things the Tories had done to improve workers’ right. That didn’t take long.

By now some opposition leaders might have begun to realise the prime minister hadn’t given him any direct answers – that there was nothing on Brexit she could say that wouldn’t risk splitting her party still further – but Corbyn stuck rigidly to his script. His questions were shorter and more forensic than usual, but lacking in passion. When it comes to Brexit, it still feels as if he is only going through the motions. As is the prime minister. She managed to ignore the Labour leader’s reference to the leaked letter from the 62 Tory MPs by insisting she was going to get a “bespoke Brexit deal”.

It was much the same with customs union and the Irish border. Corbyn asked a reasonable question, May answered something else entirely and Corbyn either didn’t notice or didn’t care enough to pick her up on it. PMQs has become so dysfunctional it’s been reduced to a divorcing couple who have become so uninterested in their relationship they can’t even bothered to have a row.

Not for the first time, Corbyn ended the session by forgetting to ask a question. May chose to indulge him with an answer, but only because she was desperate to finish with her own gag about “blank cheques” and “Czechs”. It was so feeble that even the Tory backbenchers, who had been desperate for their leader to get a few digs in about Corbyn being a commie spy, barely raised a laugh.

The one upside to all this was that the Corbyn-May exchanges, which sometimes drag on for the best part of 20 minutes, were done and dusted inside eight. Maybe they should stick to topics they would both rather avoid in the future. It’s just a shame that this one is the most pressing one facing the nation in a generation. No wonder the French MPs in the visitors’ gallery spent the whole session with large grins on their faces.