Military personnel have been part of the clean-up operation in Salisbury since last April (Picture: MoD).

More than half of the sites affected by the nerve agent attack in Salisbury have now been decontaminated, the Ministry of Defence (MoD) has told Forces News.

Sergei Skripal and his daughter Yulia were left seriously ill after being poisoned with Novichok last March.

The Department for Environment, Food and Rural Affairs (DEFRA) said that, with support from the MoD, they have handed back five of the nine contaminated sites. 

A spokesperson said:

"The decontamination process being carried out by the military and overseen by DEFRA continues for the Zizzi’s restaurant, the Mill Pub where the Skripals had a drink, their house and the home of DS Bailey who was also contaminated."

Two other people, Dawn Sturgess and her partner, Charlie Rowley, were subsequently exposed to the nerve agent, believed to have been in a perfume bottle discarded by the attackers. Ms Sturgess died eight days later.

The military has been in charge of physically doing the sampling, going in and getting them.

The Defence Science and Technology Laboratory (DSTL) at Porton Down has played a crucial role in the UK’s response to what’s happened.

Their Operations Room is currently running 18 hours a day, seven days a week in response to the further incident in Amesbury.

They have been screening over 50 people a day, analysing over 3,800 blood samples.

Across both incidents, DSTL has collected and performed chemical analysis on over 2,500 samples.

It is not clear when the decontamination process will be complete for Salisbury or for Amesbury but it is expected to take months rather than weeks.

On Thursday, the US announced it will impose fresh sanctions on Russia because it used a chemical weapon in violation of international law.

The Kremlin said the sanctions were "draconian" and denounced US action as "absolutely unlawful".

The US move was warmly welcomed by Downing Street, which has consistently blamed Moscow for the attack in March on former Russian spy Sergei Skripal and his daughter Yulia with a military-grade Novichok nerve agent developed by the former Soviet Union.