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 (March 11), 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.
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 (March 4) and Monday night (March 5).