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

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

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

This deal marked the first time in 40 years that the Kremlin released Russian political prisoners as part of a prisoner exchange.

The White House said Alexei Navalny, who died in a Russian prisoner of war camp last year, would take part in the exchange.

Kara-Murza, a father of three who survived two poisoning attempts in 2015 and 2017, said he had pushed for further exchanges with Starmer in all of his recent meetings with senior politicians, including US President Joe Biden and German Chancellor Olaf Scholz.

The deal that led to his release was an “unequal” arrangement, he said, exchanging murderers, spies and hackers for people who had not committed crimes. But there was no alternative, Kara-Murza insisted.

“There is nothing more valuable, nothing more important to democracy than human life,” he told a news conference at the Royal United Services Institute. “I know what it is like to wake up every morning in a cell that is two metres by three metres, four walls, a small window barred, and spend all day basically walking around in circles staring at walls. You have nobody to talk to, nothing to do, nobody to go to, and so the rest of your life will go on… This is not just a question of unjust detention, although that in itself would be unacceptable… it is a question of life and death in the truest sense of the word.”

Among the cases Kara-Murza referred to were 63-year-old Alexei Gorinov, an elected official of Moscow’s Krasnoselsky District Council who was the first person in Russia to be arrested for opposing the war in Ukraine, and 46-year-old Maria Ponomarenko, a journalist from Siberia who was detained for accusing the Russian Air Force of bombing a theater in the Ukrainian city of Mariupol. She is currently on hunger strike.

“We must work to get them out,” Kara-Murza said, adding that the argument that such deals encourage the Kremlin to take hostages is “wrong” since Putin will lock up his opponents anyway.

Kara-Murza, who was held in a maximum security prison in Siberia, said he also spoke to Starmer about the need for a strategic plan for post-Vladimir Putin Russia.

Authoritarian regimes appear stable from the outside, but change can happen in the blink of an eye, he said, and it is crucial not to repeat the mistakes of the 1990s after the collapse of the Soviet Union.

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

“One of the things that has been on my mind for a long time, especially in the last few weeks since I was released from prison, is that we have no right to miss the next opportunity for change in Russia,” he said.