The British government has already blamed Russia for the attack on Skripal and his daughter Yulia in Salisbury in March, citing intelligence sources as well as the independently verified identity of the poison: weapons grade nerve agent Novichok at a very high level of purity.

However this is the first time there has been a publicly revealed clue as to who wielded the poison.

The news came as an inquest was due to open into the death of Dawn Sturgess, who lived near Salisbury and appeared to have come into contact with Novichok from the same batch used against the Skripals.

The death of Dawn Sturgess, 44, from exposure to the nerve agent Novichok has added to the tensions between Russia and Britain.

Experts estimated Sturgess had been exposed to a dose ten times the amount that the Skripals had come into contact with, possibly after picking up a discarded perfume bottle in a park near Salisbury and spraying it onto her skin. The bottle containing Novichok was found in Rowley’s home in Amesbury.