Two people have fallen ill after eating in a restaurant in Salisbury, the English town where former Russian agent Sergei Skripal and his daughter were poisoned in March, police said.

"Police were called by the ambulance service to Prezzo, High Street, Salisbury at 6.45 pm today following a medical incident involving two people - a man and a woman," Wiltshire Police said in a statement on Sunday.

"As a precautionary measure, the restaurant and surrounding roads have been cordoned off while officers attend the scene and establish the circumstances surrounding what led them to become ill."