The nerve agent used to poison former Russian spy Sergei Skripal and his daughter at his home in England last month was delivered in a liquid form, the BBC reported officials as saying.

Skripal, 66, and his daughter Yulia were found slumped on a bench in the city of Salisbury on March 4.

Britain has blamed Russia for the attack which the authorities said was carried out using a Novichok form of nerve agent. Moscow denies the accusation and says Britain is trying to whip up anti-Russian hysteria.

The BBC said the Department for Environment, Food and Rural Affairs which is handling a clean-up operation in Salisbury had said a "very small amount" of Novichok was used with the substance delivered in a "liquid form".

Police have previously said they believed the poison had been applied to the front door of Skripal's modest home.

Yulia Skripal, 33, was discharged from hospital a week ago while her father is no longer in a critical condition.