Nothing about Mr. Skripal’s travels appears all that uncommon. John Sipher, who retired from the Central Intelligence Agency in 2014 and once ran covert operations against the Russians, said the United States routinely deployed Russian defectors to lecture the intelligence services of its allies, though their meetings with other agencies would be kept secret to avoid angering Moscow.
“There is a bit of a game where, O.K., the guy spied for us, we got what we wanted, and now that we’re out, we’re not going to rub your nose in it,” he said.
Sharing knowledge and experience is often the only way a former spy can make a living, experts said. Mr. Ilves, the former Estonian president, called it the “spook version of a lecture tour.”
For former double agents, retirement can be dull and anticlimactic. The British government provides a stipend, but in the past defectors have protested that it is too small. In the late 1990s, a former spy named Victor Makarov filed a complaint against the British intelligence services over his miserable living conditions and eventually ended up camping outside Prime Minister Tony Blair’s residence in protest.
Others have resorted to creative and illegal means to augment their pensions. Oleg Gordievsky, a senior K.G.B. officer whose defection in 1985 was a serious blow to the Soviet government, hosted a game show for a time. Mikhail Butkov, another K.G.B. defector, was imprisoned for three years for creating a fake business school and defrauding would-be students out of 1.5 million pounds.
“It’s psychological — they’ve been in the limelight, and they’re not important anymore,” said Stephen Dorril, the author of numerous books about Britain’s intelligence services.
Mr. Skripal appeared to be enjoying a comfortable, though modest, retirement. In Salisbury, the cozy cathedral town where he lived, the former Russian intelligence officer belonged to the Railway Social Club, drove a dark red BMW and owned a tidy red-brick home on Christie Miller Road.