The mother of British-Russian anti-Putin opposition activist Vladimir Kara-Murza is in hospital in Germany after a suspected poisoning.

Elena Gordon was taken to the isolation ward in Charité hospital in Berlin, having raised concerns on Tuesday night that she had been poisoned at Martin-Luther Hospital in the south-west of the city.

Police said they were investigating the incident as an attempted murder, with her "blood, clothing and apartment" all undergoing checks.

The police said in a statement: "The police are taking all necessary measures to ensure public security and to investigate potential suspects."

Tagesspiegel, a German newspaper, reported that Ms Gordon suspected she'd been poisoned with Novichok, the nerve agent used on Sergei Skripal and his daughter in 2018.

However, Mr Kara-Murza later said that tests confirmed his mother's fears that she'd been poisoned were not borne out. More detailed test results are expected today, according to German newspaper Bild.

A spokesman for the German police union warned that the alarm “immediately go off when an incident like this occurs, because the Russian despot has proven several times that Moscow's arm also reaches as far as Berlin and that he doesn’t shy away from eliminating critics”.

Mr Kara-Murza acquired British citizenship after moving to the UK aged 14, when Elena married a British man.

The journalist is from a long-established Russian dissident family, and went to a school in Harrow prior to attending Cambridge to read English.

The 43-year-old was detained in the Russian capital in April 2022 and was given a 25-year jail term in 2023 on charges of discrediting Moscow's army. However, he was released four months ago as part of a prisoner swap.