LONDON >> Britain offers wealthy Russians many attractions: London’s culture, bucolic countryside, exclusive schools, and a global financial hub. But for some former spies and foes of Russian President Vladimir Putin, a move west has been lethal.

Sergei Skripal, a former Russian military intelligence officer who was convicted of helping British agents and then freed in a spy swap, could become next in the disturbing pattern. Skripal, 66, and daughter, Yulia, 33, are in critical condition in England. British officials say they were exposed to a rare nerve agent.

Some lawmakers and a former top law enforcement official say the poisonings have hallmarks of deaths in the U.K. and the United States with links to Russia. They want an investigation to examine if enemies of the Russian government have been assassinated on British soil.

The deaths that have aroused suspicions include a man who was impaled on the spikes of an iron fence; a former Putin aide found in a Washington hotel room with blunt force injuries; and an ex-spy poisoned with radioactive tea.

British officials have not openly blamed the Russian government for the brazen assault on the Skripals in Salisbury. The father and daughter were found comatose on March 4 in the medieval city where Sergei Skripal had a home.

Author Joe Serio, who spent nearly 10 years with the anti-organized crime unit of Moscow’s police and wrote “Investigating the Russian Mafia,” said Britain is a popular destination for Russian émigrés because it’s “the gateway to the West, the seat of the language, the seat of the empire, the seat of major finance.”

None of that makes the country a perfect place to hide, though, Serio said.

“Russian leaders seem to go out of their way to get rid of anybody that seems to be in their way, someone who’s betrayed them, someone who’s interrupting the money flow,” he said. “They just go wherever they have to go to get their guy.”

Yvette Cooper, chairwoman of the U.K. Parliament committee that reviews police and intelligence matters, said a string of unexplained deaths must be re-examined in light of what happened to Skripal and his daughter.

Cooper cited a 2017 BuzzFeed News investigation of 14 deaths that may have involved foul play. One was Scot Young’s. He worked with Putin’s critics before his body was found impaled on railings outside his London apartment in 2014. Police treated it as an apparent suicide, although the coroner said the evidence was inconclusive.

Of all the deaths that have set off alarms, the slow poisoning of former KGB agent Alexander Litvinenko’s life is the best documented. Litvinenko, who had defected to Britain and publicly criticized Putin, died in November 2006, three weeks after drinking tea containing the radioactive isotope polonium-210.

While he wasted away on a hospital bed, the ex-spy blamed Putin. A decade later, a laborious public inquiry concluded he had been killed by Russia’s security service, “probably” with Putin’s approval.

Less clear is the 2013 death of Boris Berezovsky, an affluent Russian businessman who moved to Britain in the early 2000s and became an outspoken critic of Putin’s policies.

Berezovsky was found dead on a bathroom floor at his home in southern England with a scarf around his neck. The coroner concluded it was impossible to establish whether the oligarch was killed or committed suicide.

Doubts also have surrounded the demise of Alexander Perepilichny, a businessman who testified against Russian officials accused of stealing $230 million from a London hedge fund. He died in 2012 while jogging near his rented home.

Two autopsies proved inconclusive. Colleagues think Perepilichny was poisoned with a difficult-to-detect plant. A coroner’s inquest is underway, but no cause of death has been established.

In Washington, the District of Columbia’s chief medical examiner concluded that accidental injuries received during days of heavy drinking killed former Putin aide Mikhail Lesin. Officials never explained how Lesin got the blunt force injuries to his head and body.

The military-backed investigation of the Skripal case has transformed Salisbury into a major crime scene. Forensics tents enclose key sites such as the grave of Skripal’s son, who died last year, while police in hazardous materials gear search for clues.

British Foreign Secretary Boris Johnson has vowed to punish Russia if forensic evidence proves Kremlin involvement. But such proof could be hard to come by, Robin Niblett, director of the Chatham House think tank, said.

“The Russians have been very good at covering their tracks,” he said. “And if you don’t have clear evidence, what’s the point of going into court?”

Meanwhile, a Russian state television anchorman has warned potential double agents they should expect a shortened life span in Britain.

“Alcoholism, drug addiction, stress and depression are inevitable professional illnesses of a traitor, resulting in heart attacks and even suicide,” anchorman Kirill Kleimenov said.