Its neighbours are an Afghan restaurant, a cafe selling fried chicken and a boarded-up, Tudor-style pub. But it is from this first-floor office in north-west London that the Pakistani megacity of Karachi, 7,000 kilometres away, is remotely governed by a flamboyant and controversial British citizen.

The office is the headquarters-in-exile of the Muttahida Qaumi Movement (MQM), Karachi’s most powerful political party. Its leader, Altaf Hussain, has lived in the UK since 1991.

These days, he rarely visits his headquarters, but his portrait hangs on the wall next to coloured maps of Pakistan’s provinces, and a silver statue of a fist.

The MQM controls most of the parliamentary seats for Karachi, and has been a part of several coalition governments. But it also exercises influence through a network of heavily armed street gangs that operate in some neighbourhoods.

The party is dominated by Hussain, a charismatic figure who summons his party subordinates to meetings in London and addresses giant street rallies in Karachi, often with tens of thousands of supporters, by telephone and video conference.

His tone is fiery — and highly popular.

“We didn’t come to Pakistan to become slaves, neither are we here to become masters, we merely want to become equal citizens. If you do not like Sindhi Urdu speakers then make a separate province for them. The Urdu-speaking community knows how to cross rivers of blood... and we know how to take what is ours,” he warned this past January.

He obtained a British passport in 2002. But in recent weeks, he has been frantically requesting a Pakistani passport from officials at the High Commission in London, according to Pakistani officials.

The charges against Hussain stem from a police investigation into the death of Imran Farooq, a former party loyalist who was stabbed to death outside his home near Hussain’s office in Edgware in 2010.

Farooq had once been a close associate of Hussain’s, who publicly mourned his passing. But the two men had fallen out before his death, and the police investigation started to close in on Hussain and his associates.

The police raided Hussain’s office in December 2012 and his house in June 2013, impounding about Dh2 million in cash and arresting Iftikhar Hussain, a nephew of Hussain’s who worked as a personal assistant.

This spring, British officials asked Pakistan’s interior minister, Chaudhry Nisar Ali, for access to two Pakistani men linked to the death of Farooq. Pakistani officials said the two men were believed to be in the custody of the ISI, the country’s top military intelligence agency.

Scotland Yard named the two men and published their photographs last week, apparently in a bid to pressure the Pakistani authorities to hand them over. They were identified as Moshin Ali Syed, 29, and Mohammad Kashif Khan Kamran, 34. Both men were in London at the time of Farooq’s death and flew to Pakistan that night.

The investigation brought police scrutiny of Hussain’s finances in London. Hussain has considerable living expenses in London — his house is guarded by a private security team including former soldiers from the British army — and his party officials have scrambled to explain the sources of his funding.

Hussain has not given an interview for some years. His aides in London say he is “unwell”. YouTube footage of his British press conferences show him as a larger-than-life figure prone to wild verbal performances characterised by finger-wagging and odd gestures.

His campaign speeches are broadcast from chilly, overcast London to the Karachi faithful, many of them women who hold portraits of their tubby, moustachioed leader.

But his critics — most prominently the PTI party of former cricketer Imran Khan — accuse him of cementing his power base through increasingly violent tactics. The list of alleged crimes includes running extortion rackets, demanding protection money, carrying out targeted killings and generally menacing the Karachi population.

Back in Pakistan matters reached a head in May 2013 when one of the PTI’s best-known party activists in Karachi, Zahra Shahid Hussain, was shot outside her home.

Speaking from the MQM’s office, in Edgware, Mohammad Anwar, one of Hussain’s advisers, said the party was a legitimate democratic movement.

Hussain founded the MQM in the 1980s to defend the interests of the Muhajirs, the Urdu-speaking descendants of Muslims who moved from India to Pakistan during partition, in 1947. They arrived in a city then dominated by native Sindhis and Baloch. The MQM’s political strongholds are urban Karachi and Hyderabad, in Sindh province; it is at odds with Pakistan’s Punjabi-dominated elite, Anwar says.

But critics say that from its earliest days the party showed a readiness to use violence to fight for power. In the 1980s, when Hussain felt newspapers were giving him insufficient coverage, MQM supporters began burning all the city’s papers before they could be distributed.

“He forced all the media owners to come to the 90 [the party’s headquarters] and beg his pardon,” said Mohammad Ziauddin, managing editor of the Express Tribune. One paper protested by refusing to publish for one day.

Over the last five years, the MQM has proved to be an extremely troublesome coalition partner, temporarily walking out of the government several times and threatening to bring it down when it didn’t get what it wanted. Critics say that when political blackmail fails, it turns to street violence.

“MQM has the ability to dial up and dial down violence when certain political objectives are threatened,” said Shamila Chaudhary, a senior analyst at the Eurasia Group. “It’s not new, but now they are feeling particularly threatened in their historic domain.”

Anwar said the MQM was itself a victim of political violence because of its secular beliefs and refusal to compromise with radical Islamists. The Pakistani Taliban frequently targeted and killed MQM party workers, he said. He denied claims that the party engages in extortion, land theft and other mafia-style activities, or that it has a shadowy armed wing.

— Compiled from agencies