The most difficult thing in life – any life – is to admit you are wrong. What’s true for someone in the privacy of their own home is massively more true for the prime minister. But last Thursday, Keir Starmer made a mistake. That afternoon, the Guardian reported that Peter Mandelson had failed his security vetting and the permanent undersecretary at the Foreign Office had overruled the recommendation of UK Security Vetting (UKSV), a department within the Cabinet Office. Within the news cycle, the prime minister and foreign secretary announced they had lost confidence in Olly Robbins and he was forced to resign.

Over the past few days, No 10 has doubled down on its version of events. On Monday, Starmer told the House of Commons that, if he had known Mandelson had “failed” his vetting, he would not have allowed his posting to Washington to proceed.

Before dawn at JFK airport yesterday, I watched Robbins give evidence to the foreign affairs select committee on iPlayer while waiting for my flight to Heathrow. Emily Thornberry, the chair of the committee, and her colleagues were polite, forensic and steely. Robbins answered in the same spirit. He set out the........

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