Jeremy Hunt has warned that Brits could be at risk of being detained in Russia after it was revealed a US marine arrested on spying charges is also a UK national.

The foreign secretary’s warning came after it was revealed Paul Whelan holds dual citizenship, and had appealed to the British embassy in Moscow for consular assistance.

In a move sure to build tension between the two countries, Hunt warned the Kremlin not to use UK citizens as pawns in “diplomatic chess games”, and said government travel advice to the country is under “active consideration”.

But what “chess games” is Hunt talking about? Here’s what you need to know about the latest diplomatic spat to pit Russia against the west…

Who Has Been Arrested?

Paul Whelan, 48, is a former US marine and is currently head of global security for a Michigan-based car parts supplier, BorgWarner.

He was arrested in Moscow last week on suspicion of spying. Three days later, the Russian federal security service – the equivalent of Britain’s MI5 – said he was caught “during an espionage operation”, but gave no further details.

On Thursday Whelan was charged with espionage, meaning he could face up to 20 years in prison if convicted.

What Was Whelan Doing In Russia?

If you believe the Russian version, he was spying for the United States.

But his family have denied this, saying he was in fact in the country for a wedding.

His brother David said in an interview with CNN, Whelan had been to Russia several times previously, so when a fellow former marine was planning a wedding in Moscow, he was asked to go along to help out.

The morning of his arrest, he had reportedly taken a group of wedding guests on a tour of the Kremlin museums.

He failed to turn up for the wedding that evening, and the last time anyone heard from him was at around 5pm that day.

His family feared he had been mugged or was in a car accident, his brother said, and it was when searching the internet on Monday that he learned of the arrest.

“I was looking for any stories about dead Americans in Moscow, so in a way it was better than finding out that he had died,” he said.

What Has The US Said About The Arrest?

US Secretary of State Mike Pompeo said on Wednesday the United States had asked Russia to explain Whelan’s arrest and would demand his immediate return if it determines his detention is inappropriate.

What Has The UK Said?

On Thursday, the British embassy in Moscow was advised by its US counterpart that Whelan had told them he holds British citizenship, and therefore requested consular assistance from the UK.

Whelan lives in the US, but has British citizenship through his parents. 

Speaking during a visit to Singapore, Hunt told Sky News on Friday that “individuals should not be used as pawns of diplomatic leverage”.

He added: “We are giving him every support that we can, but we don’t agree with individuals being used in diplomatic chess games.

“Because it is desperately worrying, not just for the individual but their families, and we are extremely worried about him and his family as we hear this news.”

What ‘Chess Game’ Is He Talking About?

There is speculation that Russia could have detained Whelan because of the case of Maria Butina.

Last month Butina, a 30-year-old from Siberia, pleaded guilty in a US court to working in the US as an agent for Moscow.

She worked with a top Russian official to infiltrate a powerful US gun rights group and American conservative groups.

Russia’s ministry of foreign affairs accused the United States of forcing her to falsely confess to what it described as a “ridiculous charge”.

Daniel Hoffman, a former CIA Moscow station chief, said it was “possible, even likely” that President Vladimir Putin had ordered Whelan’s arrest to set up an exchange for Butina.

What Are The Wider Implications?

On the UK side there is the concern that British citizens in Russia could end up in a similar situation to Whelan’s.

Asked if the Foreign Office was going to change travel advice to Russia, Hunt said: “This is obviously something that is under active consideration and we’re currently reviewing our travel advice to all parts of the world and if we see the need to make a change then we’ll make it.”

This has, of course, occurred against the background of the Skripal poisonings in Salisbury last year, which the UK government has blamed on Moscow. 

Accusations made by former foreign secretary Boris Johnson that the Kremlin was behind the nerve agent poisoning of Sergei Skripal and his daughter Yulia in Salisbury last year were dismissed by Vladimir Putin.

On the US side, the case is yet another twist in the complex and ongoing saga between the two countries.

On the one hand, Russia’s relations with the United States plummeted when Moscow annexed the Crimean Peninsula from Ukraine in 2014, leading to the imposition of sanctions on Russian officials, companies and banks.

But on the other, Donald Trump’s relations with Putin have been remarkably warm, with the US president making a number of decisions during his time in office that have benefitted the Kremlin, often to the dismay of the US establishment.

This has added importance because the US special counsel, Robert Mueller, is investigating suspected Russian meddling in the 2016 US presidential election and possible collusion with the Trump campaign.

Putin told Trump in a letter on Sunday that Moscow was ready for dialogue on a “wide-ranging agenda” the Kremlin said, after a series of attempts to schedule a meeting between the leaders.