Vladimir Kara-Murza, a Russian dissident freed in the biggest prisoner swap since the cold war, has appealed to Keir Starmer during a meeting in Downing Street to not let hundreds of political prisoners in Russia and Belarus quietly “die off”.

Kara-Murza, who was released last month two years into a 25-year sentence after speaking out against the war in Ukraine, said he had told the prime minister on Friday that organising further such swaps was a matter of “life and death”.

The 43-year-old Russian politician, who has British citizenship after moving to England as a child, was one of 16 westerners and Russians, including five German nationals, exchanged last month for 10 Russian nationals, including two minors.

The deal marked the first time in 40 years that Russian political prisoners had been released by the Kremlin as part of a swap.

The White House said that Alexei Navalny, who died in a Russian prison camp last year, had been due to be part of the exchange.

Kara-Murza, a father of three, who survived two poisoning attempts in 2015 and 2017, said he had made the case for further swaps to Starmer and in all his recent meetings with senior politicians, including the US president, Joe Biden, and the German chancellor, Olaf Scholz.

The deal under which he had been released had been an “unequal” arrangement, he said, involving murderers, spies and hackers being swapped for people who had committed no crimes, but there was no alternative, Kara-Murza insisted.

“There can be nothing more valuable, more important for democracy, than human life,” he said. “I know what it’s like just to wake up every morning in a cell two by three metres, four walls, a small window covered by bars, just essentially walking in a small circle all day, staring at walls. You have no one to speak to, nothing to do, no one to go to and this is how the rest of your life is going to continue … This is not just a question of unjust imprisonment, although that in itself would be unacceptable … it’s a question, very literally, of life or death.”

Among the cases referenced by Kara-Murza were Alexei Gorinov, 63, an elected official of Moscow’s Krasnoselsky district council, who was the first person in Russia to be arrested for his opposition to the war in Ukraine, and Maria Ponomarenko, 46, a journalist from Siberia imprisoned for accusing the Russian air force of bombing a theatre in the Ukrainian city of Mariupol, who is on hunger strike.

“We need to be advocating, to be getting them out,” Kara-Murza said, adding that the argument that such deals encouraged Kremlin to take hostages was “fallacious” as Putin was going to lock up his opponents anyway.

Kara-Murza, who had been held in a high security prison in Siberia, said he had also talked to Starmer about the need for a strategic plan for Russia after Vladimir Putin.

Authoritarian regimes appeared stable from the outside but change could happen in an instant, he said, and it was vital not to repeat the mistakes of the 1990s after the collapse of the Soviet Union.

There would need to be a reckoning with those who committed crimes during Putin’s 25 years in power and a plan to reintegrate Russia into the rules-based order, he said.

“One of the things that has occupied my mind for a long time, but especially these past few weeks that I’ve been out of prison, is that we have no right to miss the next opportunity for change in Russia,” he said.