Theresa May is to chair crunch talks on the Salisbury nerve agent attack amid speculation the Government is moving closer to publicly blaming Russia.
The Prime Minister has summoned a meeting of the National Security Council (NSC) where ministers will be briefed on the latest intelligence on the incident.
She is likely to come under intense pressure to take tough action if a clear link to the Kremlin has been established.
The meeting comes as former Russian double agent Sergei Skripal and his daughter, Yulia, remain critically ill in hospital eight days after they were found collapsed on a bench in the Wiltshire city.
Detective Sergeant Nick Bailey is in a serious but stable condition in the Salisbury District Hospital, where he is said to be conscious and talking.
The NSC brings together senior ministers from relevant departments and is attended by intelligence and military chiefs as required.
Measures potentially on the table if they do decide to take action could include the expulsion of Russian diplomats and spies, new financial sanctions against individuals linked to the Kremlin, and withdrawal of official representation from the World Cup in Russia.
On Sunday, hundreds of diners and pub-goers were urged to wash clothes and other items a week after potentially coming into contact with the nerve agent.
The "precautionary advice" was issued after traces of the substance were found in The Mill pub and the nearby Zizzi restaurant, in Salisbury.
In other developments Wiltshire Police told residents "not to be alarmed" as counter-terror police were helped by Armed forces, including Royal Marines, in the clean-up operation as:
- Some eight marked and unmarked police cars were removed from Bourne Hill station in the biggest military operation yet.
- Two fire and rescue lorries were seen entering the police cordon leading to Mr Skripal's house.
- Investigators in hazmat suits bagged up items inside The Mill pub.
England's chief medical officer Dame Sally Davies said she believed up to 500 people would have been in either of the two venues between the Sunday lunchtime and Monday night.
She said: "I want to reassure the general public that the risk to us all from this incident in Salisbury has not changed, and that the risk to us all remains low."
The advice included machine wash clothing worn on the day, and double-bagging items which would normally be dry cleaned to await further advice.
Jamie Knight, 30, from Salisbury, will appear before magistrates in Swindon on Monday accused of breaching one of the cordons on Friday evening.