A Sri Lankan guerrilla leader living in London is being investigated for possible war crimes charges, The Times has learnt.

Karuna Amman, who has been implicated in atrocities over two decades, entered Britain on a diplomatic passport. The Crown Prosecution Service is looking into whether there is sufficient evidence to bring him to trial under international laws on war crimes, torture and hostage-taking.

Any prosecution would risk a serious rift with the Sri Lankan Government. His rebel group is alleged to be backed by government forces.

On Tuesday the Sri Lankan High Commissioner was called to the Foreign and Commonwealth Office to explain how Mr Karuna obtained the diplomatic passport.

He entered Britain in September and is believed to have claimed asylum after his arrest in London last month on suspicion of immigration offences.

Mr Karuna had led the Tamil Tigers in the east of Sri Lanka until March 2003 when he left to form his own group, the Tamil Makkal Viduthalai Pulikal. Among his alleged crimes are the massacre of 600 Sri Lankan police who had surrendered to him and atrocities against the Muslim minority.

In May Kim Howells, a Foreign Office minister, told the Commons that the Government believed “Karuna and his faction to be responsible for extrajudicial killings, abductions, intimidation of displaced persons and child recruitment”. The Foreign Office had a “great deal” of concern about the Sri Lankan Government’s link to him.

The Foreign Office said that at Tuesday’s meeting “we expressed our concern about how Mr Karuna was able to obtain a diplomatic passport. The Home Office and Crown Prosecution Service are looking at number of options. Because of the legal issues we are unable to discuss this any further.”

The High Commission said: “The Sri Lankan Government is unaware of any diplomatic passport or any application for a visa to enter the UK.”

Times Recommends

• The bright side of this winter rain
• Story behind the picture: Snow Leopard, 2008
• Times Charity Appeal: The Place2Be