The Government has been urged to ban Britons from travelling to Russia because of the risk of state-sponsored kidnapping after the biggest prisoner swap with Moscow since the Cold War.

Sir Bill Browder, a financier and anti-Putin activist, had fought for his friend Vladimir Kara-Murza to be released in the historic exchange.

Mr Kara-Murza, a British-Russian Putin critic, politician and journalist, was sentenced to 25 years on politically motivated charges of treason in Russia in 2023.

Sir Bill said that the law should now be changed to make sure no other British nationals fell victim to “regular” hostage-taking of foreigners, which took place with the Kremlin’s blessing.

He told the BBC’s Today programme on Friday: “We restrict it. We say that it’s no longer legal for a British citizen to travel to Russia. That’s the easy way around this.

“Are British citizens regularly going to North Korea? No. Why aren’t they? Because they do that type of stuff. Russia is the same. It’s become a totally dangerous place to go to.”

He added, “Hostage-taking is regular and we should not allow people to go to Russia anymore. It’s just as plain as day.”

Direct flights from the UK and EU were banned after Putin’s illegal invasion of Ukraine. Advice from the Foreign Office is for British citizens not to travel to Russia, where foreigners have to apply for travel visas.

Sir Bill told CNN that US and EU citizens should also be forbidden from travelling to Russia. 

Several EU member states have banned Russians from entering their territory.

Mr Kara-Murza is now set to rejoin his family in Washington but is currently in Germany after his release.

The Kremlin warned the freed prisoners to go into hiding after their release.

Dmitry Medvedev, the former Russian president, said: “Let the traitors now feverishly pick up new names and actively disguise themselves under witness protection programmes.”

The Telegraph understands that Lord Cameron, the former foreign secretary, raised the potential release of Mr Kara-Murza with the Americans more than once.

Government officials had long been involved in the discussions to have him included on any potential list as the outlines of a deal emerged.

Alicia Kearns, the Tory MP who’s also the former chair of the Commons foreign affairs committee, advocated for the British-Russian activist in discussions with the US hostage negotiation team.

The UK was always going to take a backseat in the historic prisoner swap because it couldn’t offer anyone held in Britain whom the Russians wanted, a source said.

The Foreign Office has been asked for comment.

German experts have also warned of the risk that Putin could start taking more prisoners to use as leverage in negotiations with the West.

A senior expert on hostage diplomacy who wished not to be named, told Bild tabloid: “Despite all the joy for the freed hostages and their families, as a state, we must be careful not to open Pandora’s box if Putin starts to arbitrarily arrest and convict people in order to then be able to blackmail our governments.”

Bernd Schmidbauer, the ex-hostage negotiator for former German chancellor Helmut Kohl, added: “On days like these, we are initially happy for those who have been liberated and their friends and families.

“But after that, we urgently need to talk about the dangers that now lurk. [Under Kohl] we always made sure that the negotiations took place on an equal footing and that we did not make ourselves vulnerable to blackmail in the future.”

The swap has been controversial in Germany because one of the Russian prisoners released was Vadim Krasikov, a notorious pro-Putin hitman, who gunned down a Chechen dissident while speeding through Berlin’s Tiergarten on a bicycle.

Inga Schulz, a lawyer representing the family of victim Zelimkhan Khangoshvili, said it was “devastating” that he would be free after just five years in prison.

“On the one hand we are happy that a life has been saved, on the other hand, we are disappointed that the world apparently is not based on law and order, not even in countries where the law reigns supreme,” she said.

Rising cost of hostage diplomacy

In the US, senior Republicans warned the swap “does little to discourage Putin’s reprehensible behaviour”. Mitch McConnell and Mike Johnson predicted that “the costs of hostage diplomacy will continue to rise” in a joint statement.

The two GOP leaders said: “Without serious action to deter further hostage-taking by Russia, Iran, and other states hostile to the United States, the costs of hostage diplomacy will continue to rise.

“As we renew our call for the return of all persons wrongfully detained by the Kremlin, we recognise that trading hardened Russian criminals for innocent Americans does little to discourage Putin’s reprehensible behaviour.”