LONDON: Britain will respond “appropriately” if a foreign state is found to have been involved in the poisoning of a former Russian spy in England a week ago, finance minister Philip Hammond said on Sunday.

“This is a police investigation and it will be evidence-led and we must go where the evidence takes us,” Hammond told BBC television.

“So we have to allow the police investigation to run its course. But if there were to be an involvement of a foreign state evidenced by this investigation, then obviously that would be very serious indeed and the government would respond appropriately,” he said.

Former double agent Sergei Skripal, 66, and his daughter Yulia, 33, have been in hospital in a critical condition since March 4, when they were found unconscious on a bench in the southern English cathedral city of Salisbury.

Many in British media and politics have speculated that Russia could have played a part in the attack on Skripal, but interior minister Amber Rudd said on Saturday it was too early to say who was responsible.

Skripal betrayed dozens of Russian agents to British intelligence before his arrest in Moscow in 2004. He was sentenced to 13 years in prison in 2006, and in 2010 was given refuge in Britain after being exchanged for Russian spies.

British police have said a nerve agent was used against Skripal and his daughter, but have not made public which one.

The BBC said late on Saturday that traces of the nerve agent had been found at Zizzi, an Italian restaurant where the Skripals had a meal before they were found unconscious. A police spokesman declined to comment on the report.

On Sunday, Public Health England advised anyone who had visited the restaurant or The Mill pub in Salisbury on the afternoon of March 4 or on the following day to wash the clothing they were wearing and to wipe clean personal items such as phone and handbags.

“While there is no immediate health risk to anyone who may have been in either of these locations, it is possible, but unlikely, that any of the substance which has come into contact with clothing or belongings could still be present in minute amounts and therefore contaminate your skin,” the government body said.