Altaf Hussain, the exiled leader of Muttahida Qaumi Movement (MQM), one of Pakistan's biggest political parties, was arrested on Tuesday, June 11 by Scotland Yard in London over a hate speech in 2016 in which he asked his followers to take the law into their own hands.
The Metropolitan Police would only confirm that a man in his 60s had been held in an investigation into speeches related to his MQM party.
The MQM has dominated politics in Karachi for three decades because of its support in the densely populated working-class neighbourhoods of Urdu-speaking Muhajirs, descendants of Muslims who migrated from India when Pakistan was created in 1947.
Hussain, 65, requested asylum in the 1990s and later gained UK citizenship.
But he maintains a firm grip over the MQM and its main power base, the financial capital of Karachi.
Hussain was arrested on Tuesday, June 11 morning and taken to a south London police station. Fifteen officers took part in a dawn raid at his north London home, Geo News reported.
Altaf Hussain has been arrested in relation to the hate speech of 2016 in which he had urged his followers to take the law into their own hands, it said.
His arrest was confirmed to the BBC Urdu service by his spokesman, Qasim Raza.
The police statement does not name Hussain, referring instead to "an individual associated with the Muttahida Qaumi Movement in Pakistan".
He was arrested at an "address in north-west London... on suspicion of intentionally encouraging or assisting offences contrary to Section 44 of the Serious Crime Act 2007", the statement said, adding that the man remains in custody.
Two premises are being searched, in an investigation led by the Met's Counter Terrorism Command.
It focuses on "a speech broadcast in August 2016 by an individual associated with the MQM movement in Pakistan as well as other speeches previously broadcast by the same person"