A masked woman was seen acting suspiciously in Salisbury an hour before the Skripals were found collapsed, writes dailymail.co.uk.

The dark-haired woman was spotted wearing a black face mask as she left a Pret a Manger, a three-minute walk from where Sergei Skripal, 66, and his daughter Yulia, 33, were later found convulsing and vomiting.

At the time the pair were thought to be in the Mill pub a few yards away.

Yesterday chemical warfare experts locked down a nearby village amid fears that Mr Skripal’s car could contain traces of the nerve agent that has left him fighting for his life. 

Army and police vehicles and ambulances rolled into West Winterslow just after lunchtime before investigators in hazardous material suits and gas masks loaded a white transit van on to a flatbed truck. The van’s driver was also asked to hand over his clothes, it was claimed.

The masked woman spotted on Sunday had been carrying a large bag, according to Mark Francis, a car dealer, who reported the incident to police on Wednesday.

Mr Francis said the mask could have been used to protect the identity of an assassin.

Counter-terror police have not yet released images of any potential suspects despite claims the centre of the city is covered by a new high-definition CCTV system.

Mr Francis said he initially thought nothing of the black mask, which is of the type that became a familiar sight after the outbreak of Severe Acute Respiratory Syndrome (Sars) in 2002.

But after it was revealed that nerve agents were used in the assassination attempt, he reported what he had seen.

Mr Francis, 50, said: ‘We were in the town centre in Pret a Manger. We were in there at 3.35pm and I was sitting by the door and this lady walked out at 3.40pm.

‘She was wearing a Sars mask, a black Sars mask tucked around her chin and a bag in her hand.

‘It was really odd as you don’t often see someone wearing a Sars mask in Salisbury. We don’t get smog or pollution. When it became a chemical attack it sounded more likely that it could be significant.

‘She had dark hair, a single woman, but I didn’t think she was obviously Asian.’

On Sunday it was reported that a witness told police that an hour before the couple collapsed he saw a ‘man in a mask’ with his hood up acting suspiciously nearby.

The witness said: ‘He looked threatening and aggressive and he was walking towards us with purpose. He gave me a stern look as he passed us by about 100 yards from the bench where they found the Russians.’

The white transit van which was taken from West Winterslow, five miles from the centre of Salisbury, is thought to have been used to tow away Mr Skripal’s BMW – and could also contain traces of the deadly toxin. The van was parked outside the home of Robert Horner, 22 who neighbours said works for Ashley Wood Recovery.

Mr Horner is also believed to have handed over his clothes to investigators. Neighbour Robbie Williams, 54, said: ‘They took all the guy’s clothes.’

Five specialists in breathing apparatus removed the van in a painstaking operation taking more than five hours. Earlier, counter-terrorism police including one wearing a balaclava cordoned off the top floor of a Sainsbury’s car park in Salisbury where it was believed Mr Skripal had parked his BMW before eating at a Zizzi restaurant on Sunday with his daughter.

It is thought the maroon car was taken to the Ashley Wood Recovery centre on Thursday, where it was examined by hazmat teams.