Finland, Estonia, Latvia, Lithuania and Poland have announced they will leave the Ottawa Convention of 1997, which prohibits anti-personnel landmines. Later in June, all five states are expected to give the United Nations formal notice of their withdrawal, allowing them to manufacture, stockpile and deploy such munitions from the end of the year. Together, they guard 2,150 miles of Nato’s frontier with Russia and its client state of Belarus.

Military planners are already working out which expanses of European forest and lake land would be planted with these deadly devices, laden with high explosives and shrapnel, if Vladimir Putin were to mass his forces against the alliance.

The impending return of minefields in vast areas of Europe signals the quiet demise of the international campaign to ban these weapons, famously adopted by the late Princess Diana during her visit to Angola in January 1997. “I come with my heart and I want to bring awareness to people in distress,” she said, after treading a narrow path between live mines.

Tony Blair took up the cause with such fervour that in his fourth week as prime minister later the same year, he prohibited the production and export of landmines. Britain campaigned to make this ban global through the Ottawa Convention, which was eventually signed by 164 countries. Blair even ensured that Britain ratified the Convention in time for the first anniversary of Princess Diana’s death.

One ardent supporter was Lord Robertson, the co-author of Britain’s latest defence review. As defence secretary in 1998, he condemned landmines as neither “morally correct or militarily useful” adding: “We must use Britain’s moral authority to make sure our position becomes the international standard.”

But international standards have changed since Putin launched his onslaught against Ukraine in 2022, and landmines turn out to have their uses after all.

Banning them might have been a luxury cause for a dominant West in the years of safety after the Cold War, yet no longer. Britain has not publicly opposed the decision of five allies to abandon the Ottawa Convention. Instead, as Europe re-arms to deter Putin, what was once unconscionable has become unavoidable.

Of all the countries that will now equip themselves with landmines, Lithuania’s position is perhaps the most sensitive.

The largest of the Baltic states, it must defend two hostile frontiers totalling 450 miles: with Belarus to the east and the Russian exclave of Kaliningrad to the west.