Britain signalled on Tuesday that it would not help to swap two British fighters captured by Russian forces in Ukraine for a pro-Moscow politician with close ties to Vladimir Putin.
The two Britons appeared on Russian state television on Monday and asked to be exchanged for Viktor Medvedchuk, one of Ukraine’s most powerful opposition politicians.
The wife of Mr Medvedchuk – who was arrested by Ukrainian officials – has also called for the swap in a message to British Prime Minister Boris Johnson.
The Britons, Shaun Pinner and Aiden Aslin, were captured by Russian forces after fighting for a Ukrainian unit in the besieged city of Mariupol.
Asked about the possibility of a swap, Brandon Lewis, Britain’s Northern Ireland minister, told Sky News: “We're actually going through the process of sanctioning people who are close to Putin regime; we're not going to be looking at how we can help Russia.”
He added: “We always have responsibility for British citizens, which we take seriously. We've got to get the balance right in Ukraine, and that's why I say to anybody: do not travel illegally to Ukraine.”
The UK's Foreign Enlistment Act blocks citizens from joining foreign militaries fighting countries at peace with Britain.
The government has discouraged Britons from travelling to Ukraine to fight. Mr Aslin, a former YPG fighter against ISIS in Syria, signed up for the Ukrainian military in 2018 and has a fiancée in the country. Former soldier Mr Pinner, 48, is believed to have moved to Ukraine four years ago.
Britain’s opposition Labour Party said that giving into “blackmail” over the release of prisoners encouraged more snatching of hostages around the world.
"We need to make it clear that we don't negotiate and give in to blackmail when it comes to hostages, and we've always said that we need to stick to that,” said Emily Thornberry, a senior Labour politician.
Mr Medvedchuk was arrested last week by Ukraine while he was trying to leave the country. He is considered Mr Putin’s closest ally in the country and was tipped by UK officials to be a puppet leader installed by Moscow if Volodymyr Zelenskyy was toppled.
Announcing the arrest last week, Mr Zelenskyy offered to exchange him in return for Ukrainian captives.