Up to 500 Salisbury pub-goers and diners have been told to wash possessions as a precaution after nerve agent traces were found.

Trace amounts of the substance used to poison ex-Russian spy Sergei Skripal and his daughter were found at the Mill pub and Zizzi restaurant.

Prof Dame Sally Davies, the chief medical officer for England, said the risk of harm was "low".

The advice applies to anyone in either venue after 13:30 on Sunday.

People who were at either venue before closure on Monday are advised to do the following:

- Clothes should be washed, ideally in a washing machine
- Clothes which cannot be washed, for example if they need dry cleaning, should be double bagged in plastic until further notice
- Mobile phones, handbags and other electronic items should be wiped with baby wipes, which should be bagged in plastic and put in the bin
- Other items such as jewellery and glasses should be washed with warm water and detergent
- Hands should be washed after the handling of any items suspected of being contaminated.

Dame Sally said after "rigorous scientific analysis" there was some concern that prolonged exposure over weeks and months could cause health problems but it was "not a subject for panic".

She said the advice was a "belt and braces" measure, adding: "The risk to the general public remains low and I am confident none of these customers or staff will have suffered harm."

BBC correspondent Kathryn Stanczyszyn said people in Salisbury are starting to ask why the advice had not been issued before now.

Dame Sally said it had been a "painstaking process" and the "scientific tests take time" but no harm had been caused by the wait.

Mr Skripal, 66, and his daughter Yulia, 33, are both critically ill in hospital after being found slumped on a bench in the city on Sunday.

Det Sgt Nick Bailey, who fell ill attending the pair, remains seriously ill in hospital but has been talking to his family.

The pub and restaurant are two of five sites in Salisbury focused on by investigators.

At a press conference on Sunday, Chief Constable Kier Pritchard of Wiltshire Police said he was "unable to clarify" how long those crime scenes would remain closed to the public.

A 30-year-old man has been charged with breaching a cordon at one of the sites, The Maltings shopping area, on Friday night.

He was also charged with assaulting a police officer, criminal damage to a police vehicle, common assault and a racially aggravated public order offence, and is due before magistrates in Swindon on Monday.

Also being investigated are Mr Skripal's home and the cemetery where Mr Skripal's wife and son are buried.

Soldiers are assisting police for a third day having previously helped with the removal of vehicles of interest including an ambulance.

More than 250 counter terrorism police are now involved in the investigation, which has yielded 200 pieces of evidence so far and more than 240 witnesses.

Mr Skripal, a retired Russian military intelligence officer, was convicted by the Russian government of passing secrets to MI6 in 2004, but given refuge in the UK in 2010 as part of a "spy swap".

Russia has denied any involvement.

Marina Litvinenko, widow of murdered former KGB agent Alexander Litvinenko, said Mr Skripal's case needs to be properly investigated before blame can be apportioned but it would appear lessons from her husband's death have not been learned.

After a public inquiry found her husband's 2006 assassination was likely to have been ordered by Russian President Vladimir Putin's orders, Mrs Litvinenko received a letter from Theresa May which said the government would "take every step to protect the UK and its people from such a crime ever being repeated".

Mrs Litvinenko told the BBC's Andrew Marr: "Unfortunately it happened again, it means something was not done and a lesson was not learned."

She also said Russia has a "bad reputation now" and no-one in the country had been punished for her husband's death.

Home Secretary Amber Rudd said police were "proceeding at speed" and the government was "using enormous resources" to identify those responsible for the Skripal attack.