Oh how we laughed. Oh how we tittered, as we watched through the gaps between our fingers. But it was not a joke.

Diane Abbott's performance on Sky News yesterday was a national disgrace. Labour - a once-great political party - had put up for interview, on TV and in the final days of a crucial election campaign, a politician so ill-prepared that she became a laughing stock.

Let's not forget, the Shadow Home Secretary's appearance came less than 48 hours after a terrorist atrocity on the streets of the capital and less than two weeks after a suicide bomber blew himself up at a teen pop concert in Manchester. You wouldn't have needed a department of spin doctors to work out what might come up, and yet Abbott apparently hadn't bothered to master her brief. She barely made a pretence.

Jeremy Corbyn, her party's leader, believes that this is a politician who should hold one of the great offices of state; a politician who can be trusted to be placed in charge of the police, of MI5, of the essential efforts to counter the growing threat of Islamist extremism on our streets.

Theresa May jokes about Dianne Abbott's maths, forgetting her Chancellor his sums wrong

Abbott's interview was not funny. It was the equivalent of turning up for a job interview in a tracksuit with a fag butt in your mouth, and Corbyn should be ashamed of the poor performance of an important member of his team.

It was, in fact, an insult to those who have been affected by the Manchester and London Bridge attacks. Putting Abbott in front of the cameras, in the knowledge that she might give such a poor showing of her brief, is unforgivable in the light of the events of the last two weeks.

If he is in any way serious about being our Prime Minister by the end of this week, Corbyn should replace Abbott with immediate effect. If he doesn't, he will expose himself and his cronies as the lightweight campaign group we had long suspected.