He believes that the priority of the Russian president, Vladimir V. Putin, is to “keep Ukraine bubbling,” no matter the financial costs. Mr. Pomerantsev fears that the financial pressures and Western sanctions, instead of compelling Mr. Putin to change course, are likely to make Russia more closed and dictatorial.

“What matters in a dictatorship is control of the security services and control of propaganda,” Mr. Pomerantsev said, predicting that there would be more arrests to compensate for the lack of economic progress.

“There is nothing good about the ruble crashing,” he said. “It’s just making stuff worse in Russia.”

CURLY-HAIRED, with glasses, and wearing a vest, Mr. Pomerantsev looked at home in the Legatum Institute, a liberal, free-market research institute in London that is equipped with a basement cafe for convivial debate and a book-lined library for study.

Though he grew up in West London, Mr. Pomerantsev was born in 1977 in Kiev, then part of the Soviet Union. His father, Igor Pomerantsev, is a writer, poet and broadcaster who fell afoul of the Soviet secret police, the K.G.B., for distributing works by Aleksandr I. Solzhenitsyn and Vladimir Nabokov. Encouraged to take the exit visas that were then sometimes available to Soviet Jews, the family left in 1978 for Vienna, later crossing into West Germany, where they claimed asylum. A couple of years later, Igor Pomerantsev was offered a job in the Russian service of the BBC World Service.

Apart from a brief period in Munich, when his father moved to Radio Free Europe/Radio Liberty, Peter Pomerantsev grew up as what he calls an “accidental Brit” in London. He attended one of the country’s most prestigious fee-paying schools, Westminster (the alma mater of the current deputy prime minister, Nick Clegg), but says he has still never visited large parts of his adopted country, where he lives with his Russian-born wife and three children.

At Westminster, where there was some low-grade teasing about being a Russian spy, his background generally gave him an exotic air. Though he is no Garry Kasparov, Mr. Pomerantsev’s Soviet origins were used by the school chess team to intimidate opponents. He studied English and German at Edinburgh University before being drawn by Moscow.