Four embassies will take care:

Paul Whelan: Ex-US Marine held on suspicion of spying is UK citizen
4 January 2019

Russia must not use UK citizens as "pawns in diplomatic chess", Foreign Secretary Jeremy Hunt has said, after the arrest of a former US Marine with British and American nationality.

Mr Hunt said he was "extremely worried" about Paul Whelan, who has been detained on suspicion of spying.
He added that "every support" is being given to the 48-year-old.

Mr Whelan's family said he was attending a wedding, while Russia said he was "caught spying" in Moscow.
It has been reported that Mr Whelan also holds an Irish passport.

Who is Paul Whelan?
Mr Whelan was born in Canada to British parents and moved to the US as a child. He now lives in Michigan and is director of global security for automotive components supplier BorgWarner.

He has been visiting Russia for business and pleasure for more than a decade, his brother said.

His twin David said he had been told his brother was fine and looking healthy, after US ambassador to Russia Jon Huntsman visited him this week.

https://www.bbc.com/news/uk-46756996