Coming into the event, Labour and the Conservatives had spent the day arguing over how Mr Johnson's Brexit deal might affect Northern Ireland.

Labour said a leaked document showed Mr Johnson's agreement would have a "devastating" impact on Northern Ireland.

When the subject arose in the debate, Mr Corbyn said of his rival: "He spoke at a DUP conference and said there would be no [trade] restrictions [after Brexit] whatsoever, we now know there are restrictions."

But Mr Johnson was met with applause from the audience when he said he found it "slightly curious" to be lectured about the union by Mr Corbyn, referring to the Labour leader's past support for those who want to see a united Ireland.