The attack on Skripal, a former colonel in Russian military intelligence who betrayed dozens of Russian agents to Britain's MI6 spy service, has plunged Moscow's relations with the West to a new post-Cold War low.
British Foreign Secretary Boris Johnson said late on Wednesday the Kremlin had underestimated the Western response to the attack, which also injured a British policeman.
Johnson told an audience of ambassadors in London that 27 countries had now moved to expel Russian diplomats over Moscow's suspected involvement.
"These expulsions represent a moment when a feeling has suddenly crystallised, when years of vexation and provocation have worn the collective patience to breaking point, and when across the world – across three continents – there are countries who are willing to say enough is enough," Johnson said.
Maria Zakharova, a spokeswoman for Russia's Foreign Ministry, told reporters in Moscow on Thursday Britain was breaking international law by refusing to provide information on Yulia Skripal despite the fact she was a Russian citizen.
Kremlin spokesman Dmitry Peskov said Russia was watching closely a media report that Britain might limit London's role in marketing Russian debt to investors.
Skripal, recruited by British spies while in Spain, ended up in Britain after a Cold War-style spy swap that brought 10 Russian spies captured in the United States back to Moscow in exchange for those accused by Moscow of spying for the West.
His house, which featured a good-luck horseshoe on the front door, was bought for 260,000 pounds in 2011. Skripal was listed as living there under his own name.
Since emerging from the world of high espionage and betrayal, he has lived modestly in the cathedral city of Salisbury and kept out of the spotlight until he and his daughter were found unconscious on March 4.
In the years since he found refuge in Britain, he lost both a wife and son.
The attack on Skripal has been likened to the killing of ex-KGB agent Alexander Litvinenko in Britain. Litvinenko, a critic of Putin, died in London in 2006 after drinking green tea laced with radioactive polonium 210.
Russia denied any involvement in that killing.
An inquiry led by senior British judge Robert Owen found that former KGB bodyguard Andrei Lugovoy and another Russian, Dmitry Kovtun, carried out the murder of Litvinenko as part of an operation probably directed by Russia's Federal Security Service.