Senior Tories have cast doubt on Boris Johnson’s claim that he seriously considered invading the Netherlands to seize vaccines during the pandemic, saying the story had obviously been overblown and reheated to boost sales of his memoirs. The former prime minister says in his new book, Unleashed, that he asked senior members of the armed forces about the possibility of conducting an “aquatic raid” on a warehouse in Leiden in March 2021 in order to get hold of 5m doses of the AstraZeneca vaccine which he believed the EU did not want to be exported to the UK. Johnson tells how he convened a meeting of military “top brass” in Downing Street to be told how it could be done with the use of RIBs (rigid inflatable boats) that would navigate up canals “under the cover of darkness”. He writes that after being told that it would not be possible to do this “undetected” and that the UK would then have to explain why it was invading a Nato ally, he, too, concluded that the plan was “nuts”. Ministers who worked with Johnson said they believed the plan was never seriously considered and that the former prime minister may have put forward such ideas largely as a joke, knowing he could later make the very most of them in his memoirs. They noted that the supposed plan had never been mentioned by the former PM – or anyone else – in his evidence under oath to the Covid inquiry. One former Tory minister who was very closely involved with the pandemic response told the Observer: “These were times of extreme pressure when lots of outlandish proposals were put forward, but the idea that we would invade a European neighbour was never on the table.” Another source said: “He has clearly brought this one out of the bag for his book.” The former foreign office minister Alan Duncan, who was, in effect, Johnson’s deputy when he was foreign secretary, said: “I doubt it was ever a real proposal. But given that things were so serious at that time, even if it were just a flight of fancy it is really rather worrying.” In the latest extract from his memoirs, published in the Mail on Sunday today, Johnson says he believes Covid was man-made in a Chinese laboratory. “The awful thing about the whole Covid catastrophe is that it appears to have been entirely man-made, in all its aspects. It now looks overwhelmingly likely that the mutation was the result of some botched experiment in a Chinese lab. Some scientists were clearly splicing bits of virus together like the witches in Macbeth.” Adapting Shakespeare’s words, he continues: “Eye of bat and toe of frog – and oops, the frisky little critter jumped out of the test tube and started replicating all over the world.” Johnson is expected to earn up to £4m from his memoirs.