Toxic levels of the nerve agent used to attack Sergei Skripal and his daughter could still be present at "hot spots" around Salisbury, Government scientists have warned.

A small amount of the deadly Novichok substance is thought to have been used in liquid form to target the former Russian agent, 66, and Yulia, 33.

Work is to begin decontaminating nine locations across the city where experts think the substance could still be present, in a multi million-pound operation which could take months to complete.

Officials from the Department for Environment, Food and Rural Affairs (Defra), joined local council, police and health representatives to update residents on the clean-up process at a public meeting on Thursday evening.

Asked whether the chemical remains at the same "lethal" level as the day it was put on Mr Skripal's door, Defra's chief scientific adviser Ian Boyd said: "We have to make an assumption that in certain circumstances there will be relatively high concentrations, probably in very, very specific locations, which could be at levels that could be toxic to individuals.

"That's an assumption, it's also one we've tested in some circumstances and we do know that there are hot spots like that around, so we have to make those assumptions that some of the hot spots we've still got to find.