British authorities are confident they know “everything worth knowing” about the assassination attempt on Sergei Skripal, including a trail right up to Vladimir Putin.

The Russian intelligence agency behind the Salisbury nerve agent attack has been dismantled in the UK and will remain out of action for years to come, according to government sources.

The threat posed by the GRU, which carried out the attempted assassination of Skripal last March, has been severely curtailed as a result of the counter-terror investigation that exposed the agents who carried out the attack.

Separate sources have told The Telegraph that details of the plot have been well established, including the chain of command right up to Mr Putin that gave the green light for the use of weapons-grade nerve agent on British soil.

“We are confident we know everything we need to know about Salisbury,” said the source, adding: “It will take the GRU decades to regain a foothold back in the UK.”

The GRU’s operations have been exposed in part by a series of blunders that included giving many of its agents consecutive passport numbers.