Beaufort’s Dyke is a trench, 50km long, 3.5km wide and between 200 and 300m deep, under the sea between Northern Ireland and Scotland. After the second World War, the British government decided that it was the most convenient place to dump about a million tonnes of unused conventional and chemical weapons, including sarin and tabun (both nerve gases), phosgene, mustard gas and explosives.

Nobody is quite sure what is down there: the British government told parliament in 2002 that “detailed inventories of chemical weapons and other munitions disposed of in Beaufort’s Dyke are no longer available; many records were destroyed after the disposals as a matter of routine custom and practice in view of the fact that sea dumping of munitions, including chemical weapons-filled items, was then an acceptable method of disposal”. The dyke also contains about two tonnes of nuclear waste, dumped in the 1950s.