A spokeswoman for the Home Office, Britain's interior ministry, confirmed that Vinayagamoorthi Muralitharan had been detained and was being held in a detention centre but gave no further details.
Muralitharan, also known as Colonel Karuna, is alleged to have used a false name and the title "director general of wildlife conservation," supposedly to attend a climate warming conference, the Guardian daily said.
His passport had been issued with a British visa.
Karuna was arrested by police and immigration officials in London last month and is being held in an immigration detention centre, the report said. His wife and children have already sought asylum in Britain.
Amnesty International and other groups have called for British authorities to investigate whether he can be prosecuted in Britain for international war crimes, including abducting and using child soldiers.
Karuna's paramilitary group is a breakaway faction of former Tamil Tiger rebels who switched sides and sought protection from the Sri Lankan government.
Güncelleme Tarihi: 21 Aralık 2007, 19:26