Among the performers was Jeremy Hardy, a comedian probably best known for his regular appearances on the News Quiz on Radio Four. He's a fan of Mr Corbyn and last year lamented the "extraordinary" abuse directed at the Labour leader by his oppoents.

According to Jamie Ross of BuzzFeed, who attended the event in Edinburgh, Mr Hardy's routine included a joke about Kevan Jones.

Mr Jones was the Labour shadow defence minister who resigned from Mr Corbyn's team because he supports renewing Trident and Mr Corbyn doesn't.

Mr Jones has also suffered mental illness at points of his life. Unlike a lot of people in that situation, he's spoken about it publicly, talking about his depression in the House of Commons and elsewhere.

Here's how BuzzFeed reports Mr Hardy talking about Mr Jones and Trident:

“I would have thought you could hazard a guess that if someone supports nuclear weapons, if your view of existence is so bleak you’re prepared to help with the extermination of the entire northern hemisphere, that kind of suggests depression, don’t you?” joked Hardy.

That's right, a "joke" about the mental health of a man who has suffered depression and who holds a political opinion that differs from Mr Hardy's. Hilarious, eh?