Britain's Prime Minister Theresa May stands outside The Mill pub, as she views the area where former Russian double agent Sergei Skripal and his daughter were found critically ill, in Salisbury, England, Thursday, March 15, 2018. May on Wednesday expelled 23 Russian diplomats, severed high-level contacts and vowed both open and covert action following the incident. (Toby Melville/Pool Photo via AP)

SALISBURY - British Prime Minister Theresa May visited Salisbury on Thursday, the elegant cathedral city which became the unlikely backdrop to a chemical attack against a Russian former double agent this month.

Dominated by its 13th Century cathedral with England's highest spire, Salisbury has witnessed dramatic scenes since the attack as soldiers in chemical suits and gas masks conduct forensic searches.

Dozens of passersby and schoolchildren crowded outside the city's Guildhall to get a view of May as she met emergency service workers, police and local politicians.

Most locals who have spoken to reporters have welcomed her tough stance against Russia in the affair but some worry about the effect on tourism and possible lingering health dangers.

Sergei Skripal, 66, and his daughter Yulia, 33, were found unconscious on a bench outside a shopping centre on March 4 after being exposed to what the British authorities have identified as a military-grade, Soviet era Novichok nerve agent. They remain critically ill in hospital.

The pair had visited a pizzeria and a pub before collapsing and although officials have said there is no public health danger, they have advised anyone who was in the vicinity to wash their clothes and clean all jewellery, mobile phones and spectacles with antiseptic wipes.

"I don't think these things can ever be investigated quickly, but there's sort of mixed messages," said Tommy Roberts, 50, who runs a nearby bar and hotel.

"First there is no risk to the public health, then there's a little bit, then it's 'make sure you wash everything'."

FALLING TRADE

Several local traders have noticed a drop in custom since the incident and May made a point of meeting some of them.

She visited a small clothes boutique, speaking to shop owner Sarah Haydon, who welcomed her arrival.

"We just need people to come back to the city," Haydon told reporters after May had left. "I love the city and we should promote that the city is fine."

May has blamed President Vladimir Putin for the attack and on Wednesday announced Britain would expel 23 Russian diplomats she said were intelligence agents. Russia denies any involvement.

"I was surprised at how tough she's been. I though she might pussyfoot around, but she hasn't," said Samantha Smith, 22 who works for a product design firm in Salisbury.

May said her visit was to thank emergency and health services and reassure the public about their safety.

"It's been great to meet some tourists here in Salisbury, people coming to Salisbury, still enjoying this great city," she said.

Sergei Skripal, a former colonel in Russia's GRU military intelligence service, betrayed dozens of Russian spies to British intelligence before he was arrested in Moscow in 2004.

He was given a lengthy jail term in 2006 but was released four years later as part of a swap for 10 Russian spies caught in the United States.

Since arriving in Britain, he had lived modestly in Salisbury, keeping out of the spotlight until earlier this month.