Altaf Hussain 'arrested' in London on suspicion of money laundering

Controversial leader of Karachi's Muttahida Qaumi Movement detained at home in north-west London, says his office

Altaf Hussain mourns the death of a colleague in 2010: Scotland Yard says officers are searching an address in London. Photograph: MQM party/EPA

Luke Harding and Jon Boone in Lahore

Altaf Hussain, the controversial leader of Pakistan's Muttahida Qaumi Movement (MQM), has been arrested at his home in London, according to his office in Edgware.

Scotland Yard did not name Hussain but said a 60-year-old man had been arrested on suspicion of money laundering. The arrest took place at an address in north-west London, it said, adding that officers were searching the property.

Scotland Yard said it was taking the suspect to a pre-arranged hospital appointment. "The man has an existing medical condition. He will remain in the custody of officers throughout."

Hussain is the chief of the MQM, Karachi's most powerful political party. He in effect runs the Pakistani megacity by remote control from his home 4,000 miles away.

The MQM represents the interests of Pakistan's Muhajirs, the Urdu-speaking descendants of Muslims who moved from India to Pakistan during partition in 1947. It has been a key, but frequently troublesome, coalition partner to successive Pakistani governments.

A British citizen, Hussain has lived in exile in the UK since 1991. News of his arrest led to an immediate lockdown in Karachi, with shops and businesses in the city and other parts of Sindh province closing and streets gridlocked as people tried to get home. The British high commission in Karachi also shut temporarily.

An MQM spokesman denied Hussain had been arrested. "Scotland Yard came. They asked a few questions. They have been coming for the last three years," he said. "It was a routine question-and-answer thing." Hussain was not in custody but at his home, he added.