Oh dear. When it came to getting Brexit done, Boris Johnson was, it seems, winging it more than he might have wanted to let on.

Speaking on the BBC’s Politics Live show today, Labour MP Barry Gardiner has revealed that when the former prime minister was still foreign secretary he didn’t know what a customs union was – pretty vital knowledge for, er, negotiating Britain’s departure from the EU.

Saying he could disclose the conversation now Boris was no longer an MP, Gardiner said that sometime between 2016 and 2018, Johnson stopped him in a corridor in parliament. Doing a decent imitation of Boris’s bumbling way of speaking – if Mr Steerpike may say so – Gardiner said the former PM asked him: ‘Tell me, tell me. What is all this stuff about a customs union?’

When Gardiner claims to have asked Boris what he meant by his question, Boris apparently then asked, ‘Well what is a customs union?’

Damningly, Gardiner finished off his anecdote by referencing the chaotic Northern Irish backstop Johnson was responsible for negotiating. ‘He did not know, as the foreign secretary, what a customs union was, and that explains why we got into the problems that we then got into with Northern Ireland.’ Ouch!

Boris Johnson said to me, “what is a customs union?”

Labour MP Barry Gardiner recalls a conversation with the former PM, saying he “did not know as the foreign secretary what a customs union was” #PoliticsLive https://t.co/1BfD7R35CC pic.twitter.com/jgHB7nZzTz

— BBC Politics (@BBCPolitics) September 11, 2023