Leader of the breakaway faction of the Tamil Tiger rebels Vinayagamoorthy Muralitharan alias Colonel Karuna was arrested in London on Friday.
He was arrested for traveling on a forged passport, Home Office sources said.
Karuna has been blamed for attacks against the Tigers since his split from the LTTE in March 2004.
LTTE leaders say he is working for the Sri Lankan government to disrupt their operations. The Tigers also accuse the government of protecting Karuna and his loyalists to carry out attacks against their supporters.