Theresa May leaving Salisbury Cathedral during the visit on Monday (Picture: PA).
The Prime Minister has praised the "tremendous spirit and resolve" shown by the people of Salisbury a year on from the nerve agent attack in the city.
During a visit to Salisbury, Theresa May met some of the neighbours of the former Russian spy Sergei Skripal.
"This city has shown such spirit and resolve in the last 12 months," said Mrs May.
"The impact of the utterly reckless use of a nerve agent should not and will not be forgotten."
Up to 800 military personnel were involved in Operation Morlop - the name of the military response to the nerve agent attack.
The military was first deployed last April in response to the incident with around 190 personnel making Salisbury safe to the public, completing work near the Maltings area of the city the following month.
The clean-up has been taking place ever since the attack ten months ago, but work paused over Christmas.
In September 2018, UK forces were deployed to decontaminate Mr Skripal's home.
Former Russian spy Sergei Skripal and his daughter Yulia were poisoned with Novichok, a nerve agent, in Salisbury, Wiltshire.
The Russian GRU intelligence agency has been blamed for the use of the chemical weapon.
Following the attack on the Skripals, residues of the nerve agent in the area later claimed the life of Dawn Sturgess.
Ms Sturgess died after coming into contact with a perfume bottle believed to have been used in the attack on the Skripals and then discarded.
She had also visited businesses in the city and its historic cathedral following last week's announcement that the clean-up operation at sites connected with the attack had been completed.
"It is incredibly heartening to see the hard work and determination of the people here to ensure this city has a positive and prosperous future, which it deserves," said Mrs May on her visit.
Foreign Secretary Jeremy Hunt thanked the UK's allies for their response to the attack.
The UK expelled 23 diplomats it claimed were Russian spies following the attack and other Western powers followed suit.