The bodies of Russian dissidents who died mysteriously could be exhumed in the wake of Boris Johnson’s disclosure that the Kremlin has spent a decade developing nerve agent for assassinations.

The remains of at least two Russians who dropped dead suddenly in the UK are now expected to be re-examined. Neither were tested for nerve agent poisoning at the time they died.

On Sunday Mr Johnson, the Foreign Secretary, accused Vladimir Putin’s regime of breaking international law by developing the nerve agent Novichok for use by hit squads over the past ten years.

Sergei Skripal, a Russian spy, and his daughter Yulia Skripal are fighting for their lives in intensive care after being poisoned by Novichok in Salisbury, Wiltshire, a fortnight ago.

On Monday inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) will visit the defence laboratory at Porton Down to collect nerve agent samples used in the attack and send them for independent testing. Results, however, will take at least two weeks.