Experts wearing protective suits were drafted in to Salisbury as the investigation continued. Areas of interest were the graves of Sergei Skripal’s wife and son, which may have been visited by him on Sunday

Sergei Skripal was a highly paid, highly valued MI6 spy codenamed “Forthwith” who provided important material to British intelligence over a ten-year period, including the entire telephone directory of the GRU, Russian military intelligence, The Times has learnt.

As investigations continue into the poisoning of Mr Skripal, 66, and his daughter in Salisbury on Sunday, this newspaper has been able to build a picture of his recruitment and work as a double agent for MI6.

Mr Skripal during his time with the Russian military

He was spotted as a potential recruit by the Spanish intelligence service but run by UK intelligence as it was believed he would respond better to British handling. Stationed in Spain as a GRU officer, Mr Skripal was approached around July 1995 by an MI6 officer posing as a commercial