It has been revealed the Salisbury nerve agent was 'delivered in liquid form'.

Former Russian double agent Sergei Skripal and his daughter Yulia were found slumped on a park bench on March 4th, after being exposed to the novichok nerve agent.

British officials say Mr Skripal's Wiltshire home - situated on the outskirts of Salisbury - was targeted with a "very small amount" of novichok.

A spokesperson for the UK's Department of the Environment (DEFRA) explained:  "In this instance, direct contact is required for a person to be poisoned. Only a small proportion of the material is transferred in each contact and the substance is diluted in each secondary or tertiary contact.

"The class of nerve agent does not produce significant vapour or gas and can only be moved between sites by direct transfer from a contaminated person or by moving a contaminated item."

Clean-up operation

It comes as as a massive clean-up begins at nine potentially contaminated sites in Salisbury.

The operation - which will involve 190 specialist military personnel - will take several months and cost millions of pounds.

Sites identified for contamination include a pub, ambulance stations, and the home of a police officer believed to have been exposed to novichok.

A previously cordoned-off area of a cemetery where Mr Skripal's wife and son are buried has reopened to the public today, after clean-up teams confirmed it had not been contaminated.

In a statement, Wiltshire Council leader Jane Scott said: "Working together with local and national agencies we are doing all we can to help Salisbury return to normal.

"Our main concern is to ensure that Salisbury is safe for residents, businesses and visitors and that the city can focus on the future, its recovery and that it will go from strength to strength."

The operation will involve chemical cleaning and repeated testing, with locals being told they will see 'more activity' in the city as the clean-up work gets under way.

Last week, the Organisation for the Prohibition of Chemical Weapons (OPCW) confirmed the UK's findings that the novichok nerve agent was used in the attack.

The UK has accused Russia for being responsible for the attack, while Moscow has repeatedly denied any role in the attack.

Yulia Skripal was discharged from hospital last week, more than a month after the attack.

Her 66-year-old father is said to be recovering 'more slowly' but is expected to also be discharged 'in due course'.

Additional reporting by IRN