MQM founder Altaf Hussain was summoned to the Scotland Yard office for questioning Thursday morning.
He is being investigated in a case regarding a speech he made in London in August 2016 that was broadcast in Pakistan. The speech incited violence and maligned state institutions.
As a result of the incendiary speech, cases were registered against the MQM founder and several party leaders in Pakistan. The party later split into two and the leaders distanced themselves from Altaf.
Pakistan approached the UK seeking action against the MQM chief there too.
The police took Altaf into custody in June and then released him on bail. His bail was extended once.
MQM London leaders say the summons is per routine and that if Altaf had to be charged, it would have happened earlier. However, there are chances that Pakistan found new evidence in the case and has shared it with the British police.
Altaf was summoned at 9am and as of 10:30am British time, was still at the police station.