The mother of Mikhail Khodorkovsky - the billionaire oligarch locked up for defying Vladimir Putin - has appealed to the British Foreign Secretary, David Miliband, to raise her son's case during his high-profile visit to Russia today and tomorrow.

Khodorkovsky's mother, Marina Filipovna, 74, said she was "deeply concerned" by the United States Administration's new hands-off approach to Russia - and said it was essential Britain kept human rights at the forefront of its dialogue with the Kremlin.

"It's very important that Western leaders keep raising my son's case."

Asked whether Russia was likely to heed criticism from Miliband, given London and Moscow's recent fraught relations, she replied: "Foreign governments have enough levers that they can use."

Miliband was to arrive in Moscow today on his first visit to Russia as Foreign Secretary. The date coincides with the third anniversary of the poisoning in London of former Russian agent Alexander Litvinenko, which thrust British-Russian relations into a period of turmoil from which they have not yet fully recovered.

Filipovna said she was "alarmed" by US Secretary of State Hillary Clinton's recent visit to Russia and the apparent downgrading of human rights issues by President Barack Obama. "During a radio interview Clinton was twice asked about my son's case. She refused to comment."

Once Russia's richest man, and chief executive of the country's biggest oil company Yukos, Khodorkovsky was dramatically arrested in October 2003 on the runway of a Siberian airport.

The criminal case against him was widely seen as punishment for his decision to fund opposition parties and to challenge the might of then-President Putin. Khodorkovsky was jailed for eight years for fraud and other offences.

In 2007, prosecutors filed fresh charges against Khodorkovsky and his business partner Platon Lebedev. For the past seven months both defendants have appeared in court in Moscow, sitting in a heavily guarded bulletproof glass cage.

Supporters say this second trial is groundless, contradictory and increasingly surreal. This second case - on charges suspiciously similar to the original ones - has caused consternation in the European Union. The European Court of Human Rights will soon rule on the question of whether the Russian state was entitled to grab Yukos' assets.

Asked why the Kremlin had singled out her son for punishment, Filipovna said: "Obviously there was some sort of political motivation behind it, even though my son never harboured any political ambitions. But more importantly, people were trying to get hold of his property and ... his money."

Khodorkovsky was surviving his ordeal surprisingly well, she said.

Russia's President, Dmitry Medvedev, has repeatedly called for an end to his country's "legal nihilism". Some optimists believe he is sincere in his stated desire to reform the country. Khodorkovsky's second trial is widely seen as emblematic: observers ask if Russia wants to re-engage with other countries or continue its Putin-era slide towards autocracy and contempt for the rule of law.