“He had suffered from pancreatitis and gallstones and had been found with broken fingers and bruising to his body, the Kremlin's Human Rights Council said in July 2011. There were, it said, grounds to suspect that he had died as a result of a beating,” the BBC added in background to the news that the Russian Investigative Committee's lead investigator, Marina Lomonosova had written to Magnitsky’s mother saying: "The crime committed by [Dr Litvinova] is an inadvertent act for which the maximum sentence does not exceed three years. Currently, the crime... is considered by law as a crime of insignificant severity, for which the statute of limitation constitutes two years."

Dr Litvinova was the head doctor at Butyrka maximum security prison in Moscow where Mr Magnitsky died in November 2009.

The United States and Netherlands have placed a visa ban on 60 Russian officials linked to Magnitsky's death. Swedish lawmakers requested their government to press for a European asset freeze and travel ban on Russian officials. British lawmakers urged the implementation of similar sanctions.

William Browder’s London lawyers, Peters and Peters are questioning the apparent leaking of a Hermitage Capital executive’s London home address to Russian officials implicated in the suspected murder of Magnitsky.

Newly disclosed court documents suggest the Serious Organised Crime Agency (Soca) passed confidential information to staff at Russia's interior ministry, who are accused of being involved in the death of Magnitsky.

Now a senior employee of Hermitage – who has already received a number of death threats from Russia – claims his family has been placed in danger by the apparent collusion between UK police and Russian interior ministry officials.

In the two years since Magnitsky's death, senior Hermitage staff have received death threats that prompted them to contact Scotland Yard's counter-terrorism unit, SO15, who offered security in case they were targeted by Russian hitmen operating in London.

In turn, Soca alerted Interpol with its concerns about the case and warned that any extradition request by the Russian Federation or other attempts to arrest Hermitage staff "should be declined".

Yet despite the official assurances that it would not co-operate with the Russian authorities, evidence has emerged suggesting that Soca has leaked the London address of Hermitage executive Ivan Cherkasov – the subject of not only death threats but an arrest warrant from a Russian official implicated in the alleged tax fraud – to the country's interior ministry. One document says: "Based on the information from the National Central Bureau of the UK [part of Soca], the above stated individual [Cherkasov] is residing at his home address [details enclosed]."

The documents were sent from staff at Russia's interior ministry to an individual named as among those who, it is claimed, prevented Magnitsky's lawyers from seeing their client shortly before his death. The same official is part of a group of 60 Russian officials banned from entering the US for their alleged involvement in Magnitsky's death.

Browder, who campaigns to have Magnitsky's killers brought to justice, is quoted in the British press as saying, "It is incredible that there has been collusion between British police and individuals who are effectively criminals."

Last month MPs passed a binding resolution calling on Britain to ban and freeze the assets of the officials linked to the Magnitsky case. Foreign Office minister David Lidington said the government is "carefully considering" the call.

The renewed publicity in Britain over the Magnitsky case coincides with what is described as “a new period in Anglo-Russian co-operation in the fight against organised crime with Soca officials recently in Moscow to discussing the re-opening of its bureau there to liaise with Russian crime fighters over drug and human trafficking and internet crime. The British initiative came in the wake of the attempted murder of Russian businessman German Gorbuntsov near Canary Wharf.

If the Magnitsky stain is not wiped clean these cooperative efforts could be de-railed and Russia’s reputation as a country plagued by prison abuse and widespread corruption will continue to damage Russia’s relations with its partners. All the considerable efforts to act against police abuse and corruption under the Medvedev presidency are as nought in the eyes of the world until a complete open investigation into Magnitsky’s tragic death brings thos responsible to justice.