On and on he went, his voice growing louder and more defiant with every success he cited. “I could go on all afternoon,” he cried. Some people started applauding – and then more, and more, until most of the hall was at it.

One man, however, did not join in. The party leader. While members rose in their hundreds to acclaim Mr Watson, he sat in his chair, staring stonily.

“I don’t know why we’ve been focusing on what was wrong with the Blair and Brown governments,” concluded Mr Watson, pointedly. “But trashing our own record is not the way to enhance our brand.”

Funnily enough, Mr Corbyn didn’t applaud that, either.

His devotees were now heckling Mr Watson in numbers. “What about Chilcot?” shouted one woman.

Mr Watson turned calmly to face his leader. “Jeremy,” he said, “I don’t think she got the unity memo.”

Most of the hall laughed. Mr Corbyn did not. His deputy had made a joke at the expense of both him and his supporter. He was conspicuously unamused. The tension was excruciating.