There was a strange through-the-looking-glass feel to a BBC television debate this week between Britain’s Conservative prime minister, Rishi Sunak, and his Labour challenger, Sir Keir Starmer.

Starmer is the man flying high: his commanding lead in opinion polls suggests that on July 4 he might deliver the largest parliamentary majority the 124-year-old Labour Party has ever known. Sunak is the man brought low: buffeted by scandals, crises, friendly fire, misjudgments and missed opportunities, he has set the Tories on course for a historic, possibly even existential, defeat.