A short walk from Salisbury’s medieval cathedral and narrow lanes of boutique shops, a group of restless homeless people are gathering outside the city’s only remaining hostel in the searing heat of the sun.

Josh Harris has little more than his tracksuit bottoms and his beloved dog. Everything else he owns is inside the John Baker House hostel, which was suddenly evacuated on Thursday as authorities rushed to cordon off areas frequented by the couple at the centre of Salisbury’s latest nerve agent poisoning.

“We couldn’t go back into John Baker to grab anything. I’ve lost the lot. Everything in that building is going to be stripped out,” he says fiddling with a lanyard on his skinny bare chest.

The victims, Dawn Sturgess and her partner Charlie Rowley, stayed in her room in John Baker House before they became critically ill last weekend. The nine-bedroom hostel is one of the places the authorities suspect the couple may have come into contact with novichok, which put a former Russian spy, Sergei Skripal, and his daughter, Yulia, in hospital in March.

The latest poisoning has revealed a side of Salisbury the city’s nervous tourist industry prefers hidden: a desperate world of rough sleepers, hostels, heroin addicts shooting up in car parks and street drinkers.

Harris knew the couple, who are still being treated at Salisbury District Hospital, well and says they were well liked. Sturgess, in particular, was regarded as the “mother of the hostel” as she always had time to talk through everyone’s problems.

Forensic investigations continue, and police are trawling through 1,300 hours of CCTV footage

“She will help you out if you are feeling low, talk with you to try to alleviate what is the matter, try to put you in a better frame of mind,” he says as his dog pulls on the leash.

The couple had their own problems. They were known to local services but were beginning to grapple with their demons. “Dawn and Charlie are lovely people. Dawn drinks and Charlie is trying to get himself clean from heroin,” says Harris.

The evacuation of the shelter has left many of the city’s homeless people anxious. Harris was seen by specialists after he also fell ill last weekend, around the same time as Rowley and Sturgess. “I had diarrhoea and vomiting on Saturday morning. I was in hospital from Saturday evening until Sunday morning. I was checked by Porton Down scientists and thankfully I got the all-clear,” he says.

Theories are circulating about how the couple may have come into contact with novichok. Forensic investigators were continuing to search on Saturday for any sign of the item that could have contaminated them, and police officers were trawling through 1,300 hours of CCTV footage.

Harris thinks that Rowley may have touched the vessel containing the deadly nerve agent while “bin diving” – retrieving unwanted electrical items from wheelie bins to sell at the local Cash Converters.

“He goes bin diving like a lot of people do. But now after what has happened I’m not going,” he says.

After publication of this article, Cash Converters told the Guardian that it had checked CCTV and neither Sturgess or Rowley had appeared in its Salisbury store selling items, themselves or as companions of others doing so, in or around the time of the poisonings in March or since. Account records showed that neither Sturgess nor Rowley had sold items at the local Cash Converters for at least two years.

The last time Harris saw Sturgess was on the Friday morning. “She wasn’t herself whatsoever. She was confused, spaced, not with it,” he says.

Forensic investigations continue on Muggleton Road, Amesbury, eight miles from Salisbury, at and around the home of victim Charlie Rowley. Photograph: Matt Dunham/AP

Shane Phillips, who also lives at Alabaré Place, where Josh Harris and others from John Baker House have been moved, has known Rowley since he was a young man.

“He got quite a bad habit when he was young but he would do anything for you. He was a nice bloke. He had a heart of gold.”

Rowley was staying at Alabaré Place until the council found him accommodation eight miles away in Amesbury, which has also now been sealed off by police. Phillips says: “He was really happy because he was moving from place to place not knowing where he was going to be.”

Phillips says that hard drugs are readily available in Salisbury. “I was living under the Maltings car park when all this first happened in March. I’d say there were 40 or 50 addicts in that car park. Salisbury’s got a big problem,” he says.

Some might say this is a genteel, picture-postcard sort of place but we have the same challenges as other urban areas Matthew Dean, Salisbury council leader

None of this comes as a shock to the affable Conservative city council leader, Matthew Dean. “Some people might say this is a genteel, picture-postcard sort of place but we have the same sort of challenges as other urban areas,” explains Dean, sipping a pint of cola in a city centre pub. “It’s not the Bronx or a sleepy cultural backwater either. The truth’s somewhere in the middle.”

He accepts that the city has a homeless and drugs problem, although no more than other towns and cities. “Salisbury has a historic problem because people come here because the footfall is so much higher than other market towns in Wiltshire.

“We’ve also issues with veterans suffering from post-traumatic stress disorder.”

Dean adds that in recent years there has been a growth in “county lines” dealing, where gangs attempt to move drugs into new markets. “We do not have a drug epidemic. But what we have seen is a bit of county lines drug dealing, with people coming from Southampton, Portsmouth, London and Birmingham finding people that are vulnerable and getting drugs to them.”

Yet Dean, who is also a Wiltshire county councillor, is keen to stress that Sturgess and Rowley were being helped to turn their lives around. “These two individuals were textbook examples of Wiltshire council’s approach to helping people,” he says.

“He was successfully rehoused. She had been sofa surfing and she’d been found hostel accommodation. They were well on the way to having ordered lives and being able to look after themselves.”

• This article was amended on 12 July 2018 to add information received from Cash Converters after publication.

