The AstraZeneca vaccine was, at the time, at the heart of a cross-Channel row over exports, and Johnson believed the EU was treating the UK “with malice”.

Johnson said that he “had commissioned some work on whether it might be technically feasible to launch an aquatic raid on a warehouse in Leiden, in the Netherlands, and to take that which was legally ours and which the UK desperately needed”.

The deputy chief of the defence staff, Lt Gen Doug Chalmers, told the prime minister the plan was “certainly feasible” and would involve using rigid inflatable boats to navigate Dutch canals.

“They would then rendezvous at the target; enter; secure the hostage goods, exfiltrate using an articulated lorry, and make their way to the Channel ports,” Johnson wrote.

However, Chalmers told Johnson it would be difficult to carry out the mission undetected, meaning the UK would “have to explain why we are effectively invading a longstanding Nato ally”.

Johnson concluded: “Of course, I knew he was right, and I secretly agreed with what they all thought, but did not want to say aloud: that the whole thing was nuts.”