Russian officials involved in corruption and human rights abusers are to be targeted with a tough sanctions regime coordinated with Britain, the US and Canada.
Boris Johnson, the Foreign Secretary, and Amber Rudd, the Home Secretary, have agreed that Britain will introduce a UK version of the so-called "Magnitsky Act" under which 49 Russian nationals are named in an official US list of "gross violators of human rights", whose crimes include extrajudicial killings and torture.
The move, which was being planned before last week's poisoning of Sergei Skripal, a former spy, and his daughter Yulia in Salisbury, is likely to inflame tensions with Moscow, after the nerve agent attack that Government figures believe points to Russian involvement.
If evidence points towards Russian involvement in the attack, Prime Minister Theresa May could choose to announce the new laws as part of a raft of retaliatory measures against Moscow. Russian President Vladimir Putin has railed against similar legislation introduced in other countries.
British police have identified more than 200 witnesses and are looking at more than 240 pieces of evidence in their investigation into the attack.
Former double agent Skripal, 66, and Yulia, 33, have been in hospital in a critical condition for a week.
"The two victims remain in hospital and they're critical but stable," Rudd told reporters.
In Salisbury, normally a quiet city, military vehicles and troops in protective suits and gas masks were seen working at several of the sites associated with the Skripal investigation. At an ambulance station a short distance from the city centre, troops in light grey overalls, purple gloves and gas masks covered ambulances with black tarpaulins as they prepared to remove them. At the hospital where the Skripals were being treated another team used an army truck to remove a police car.
Rudd told reporters that Nick Bailey, a police officer who became unwell after taking part in the early response to the attack, remained seriously ill but was talking and engaging with his family. "He does not consider himself a 'hero', he states he was merely doing his job," a police statement said.
Rudd said more than 250 counter-terrorism police, from eight out of Britain's 11 specialist units, were involved in the investigation.
There was also a flurry of activity at the cemetery in Salisbury where Skripal's wife and son are buried, with forensic teams active in several parts of the site. Skripal's son, Alexander, died in July last year at the age of 43. British media reported that he died while in St Petersburg, Russia. Skripal's wife, Liudmila, died of cancer at 60, in 2012.