If politicians learn one lesson from the events of 2016, let it be this. Never give a speech about Brexit on an empty stomach.

Because, however valiantly you try to soldier on, it’s practically guaranteed that at some point you’ll accidentally call Brexit “breakfast” instead.

Look what happened to poor Andrew RT Davies, the leader of the Welsh Conservatives, during his mid-morning speech at Tory party conference this month. He intended to cry, “We WILL make Brexit a success!” Instead he cried, “We WILL make breakfast a success!”

Still, at least he only did it once. In a speech in London at 11 o’clock this morning – that dangerous hour, when the blood sugar is running low and the stomach is starting to growl – Labour’s John McDonnell did it not once, not twice, but three times.