Sergei Skripal and his daughter Yulia remain critically ill after being found unconscious in Salisbury this week.
Home Secretary Amber Rudd has visited the scene where former double agent Sergei Skripal and his daughter were found after they were targeted in an "outrageous" chemical attack.
"Russia's being assertive, and we have to change the way that we deal with it because we can't be in a situation in these areas of conflict where we are being pushed around by another nation", said Williamson.
A spokesman for British Prime Minister Theresa May said the poisoning was an "appalling and reckless crime".
Hundreds of investigators, led by counter-terror police, are working to find out who is responsible for what is feared to be a sophisticated plot amid heightened tensions between Britain and Russian Federation.
Calling it a "tragic situation", Putin's spokesman Dmitry Peskov said the Kremlin had no information about the incident.
Sergei Skripal, 66, and his daughter Yulia remained in critical condition, while police officer Nick Bailey, who was the first to go their help on Sunday and was exposed to the nerve agent, is recovering in hospital from his serious condition. "The profession of traitor is a lot more unsafe than that of a drug courier".
On Thursday night, an eyewitness said police had been searching a auto at a vehicle recovery centre close to the Russian victim's home earlier that day.
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"But in order to have a serious conversation. you have to use the official channels". This work was carried out at the UK's defence laboratory at Porton Down using samples of the agent isolated from the victims' blood. The Kremlin has repeatedly denied any involvement in Litvinenko's killing. "So there is the ideal excuse for Britain to do nothing, and pretend it hasn't seen anything", he added.
Skripal betrayed dozens of Russian agents to British intelligence before his arrest in Moscow in 2004. He died agonizingly slowly after drinking tea at a London hotel that was laced with radioactive polonium-210. Thus she commented on the attack on former Main Intelligence Directorate (GRU) Colonel Sergey Skripal in Salisbury on March 4. Skripal ended up in Briatin as part of a spy swap.
The involvement of "a British citizen, especially a policeman, requires the immediate and strong involvement of the British authorities", Chatham House analyst Mathieu Boulegue told AFP. About $300 billion in cash and assets are estimated to be in the United States.
However, the Russian FM pointed out that Litvinenko's death, also blamed on Russia, hasn't been fully investigated.
FILE - The grave of murdered ex-KGB agent Alexander (Sasha) Litvinenko is seen at Highgate Cemetery in London, Britain, Jan. 21, 2016.
Among the possible responses, Boulegue said Britain could impose "a more restrictive visa regime for Russians close to power". An estimated 500 Russian multimillionaires live in Britain.
"I can reassure the House that, should evidence emerge that implies state responsibility, then Her Majesty's government will respond appropriately and robustly", Johnson said on Tuesday in an urgent question session at the House of Commons. Critics say as a further step, the government needs to insist Caribbean tax havens clean up their act and introduce rigorous transparency rules.
To have used such a volatile toxin, in a public place, knowingly endangering anyone who would come to the aid of the seriously ill father and daughter, is beyond comprehension. Russian media said his motivation was financial: he received more than $100,000 paid into a Spanish bank account. Brexiters have been calling for greater deregulation of the city of London. Rhondda MP Chris Bryant, who chairs the all-party Parliamentary group on Russian Federation, said it would be "very difficult" for the England team to compete in the World Cup in Russian Federation this summer if Moscow is linked to the attack. This year's World Cup competition being hosted by Russian Federation is likely to be a target for some kind of boycott, say officials.