The Southern English city of Salisbury was the subject of a major security scare on Sunday night amid fears of a possible poisoning at a local restaurant.

Salisbury and the surrounding area have been in the spotlight in recent months ever since former Russian double agent Sergei Skripal and his daughter Yulia were exposed to nerve agent Novichok in the city center in March.

In June, two residents of the nearby town of Amesbury fell ill after being exposed to the same substance. One of them, 44-year-old Dawn Sturgess, subsequently died, and a murder inquiry is now under way.

Wiltshire Police declared a major incident on Sunday after two diners were taken ill at the Prezzo restaurant, and subsequently taken to hospital, but they are no longer treating the incident as major and have lifted security cordons around the restaurant.

An eyewitness told the BBC that one of the diners, a woman, appeared to be repeatedly getting up from her table and returning, before the situation became more serious.

"She was hysterical. She called paramedics and the next thing an ambulance turns up and they come rushing in and then they rush out again," said the witness.

Five ambulances, members of the fire service and 12 police officers attended the incident. The couple remain in Salisbury District Hospital under observation, but no more details of their condition or identities have been made public.

"Due to recent events in the city and concerns that the pair had been exposed to an unknown substance, a highly precautionary approach was taken by all emergency services," said a statement from Wiltshire Police, who assured the public that there was "nothing to suggest" Novichok was the cause of the latest incident.

The Skripal incident caused a major diplomatic dispute between London and Moscow, with more than 20 other countries, including the United States, Canada and 18 European Union member states joining the United Kingdom in expelling Russian diplomats.

The British government has accused the Russian government over the attack on the Skripals, something Moscow has consistently denied.

Britain has identified and named two Russian men seen on security camera in Salisbury in connection with the attack, Alexander Petrov and Ruslan Boshirov, and issued a European Arrest Warrant for them, but in an interview on Russian television last week, the pair claimed to be innocent tourists.