Farrugh Naseem, representing former military ruler General (retd) Pervez Musharraf in treason case, left for London with senior MQM leader Rauf Siddiqui.
"My job is to go and provide all legal assistance to Altaf Hussain. Let us be clear he has not been charged in any case as yet by the British authorities," Naseem told PTI.
There was some relief for the hundreds of MQM supporters who are on streets since Hussain's arrest on Tuesday.
His London residence was raided on money-laundering suspicion in 2012 and 2013 by British police.
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MQM leaders confirmed that the British government has now allowed the Pakistani High Commission in London access to their leader who is still hospitalized for various ailments.
Imran Mirza, the acting Pakistani high commissioner to the UK, met with Hussain at the Wellingdon hospital where the MQM leader is under treatment.
Mirza said Hussain was in high spirits, adding that the MQM chief thanked the prime minister and the Pakistani public for their support.