By Alastair Lawson
BBC News, London
Altaf Hussain is one of Pakistan's most powerful political exiles
At first sight it may appear that there is not much to link a nondescript office block in the heart of north London suburbia with the leadership of one of Pakistan's most influential political parties.
But it is from the somewhat drab streets of the London Borough of Barnet that hundreds of thousands of people in the country's largest city, Karachi, receive their orders.
The "International Secretariat" of the Muttahida Quami Movement (MQM) is based in the suburb of Edgware, and from the first floor of a grey tower block their leader, Altaf Hussain, addresses huge audiences in the southern port city.
Mr Hussain says he lives in London because he fears he would be assassinated if he went back to Pakistan.
The party mostly comprises - and is supported by - the families of Muslim Urdu-speaking people known as Mohajirs who migrated to Pakistan from India around the time of partition.
Mr Hussain speaks to his supporters by a conference telephone connected to loud speakers strategically located across Karachi.
At least 41 people died in street battles over the weekend
Thousands of people down tools to listen to his regular addresses from London, even though he has not been back to the country since 1992 - and some of his "sermons" have been known to last longer than four hours.
The MQM's presence in Britain has become more controversial of late because of weekend violence in Karachi in which at least 40 people were killed.
Opposition parties say that much of the violence was orchestrated by the MQM's leadership in London. They allege that the party called its supporters out onto the streets to defend President Musharraf's decision to suspend the country's Chief Justice, Iftikhar Muhammad Chaudhry.
The MQM - which is allied to President Musharraf's supporters in the Pakistani parliament - is alleged to have mobilised a large body of supporters to prevent the chief justice from leaving the airport when he visited Karachi on Saturday.
In the worst violence, supporters of the party clashed with activists from the Pakistan People's Party (PPP) of former Prime Minister Benazir Bhutto in gun battles that lasted longer than an hour.
MQM members are alleged to have shot at opposition protesters holding a march in support of the dismissed chief justice, killing at least five people.
"I can absolutely deny that our supporters were involved in any of the violence," says the party's London-based senior co-ordinator, M Anwar.
"We were the only party in the city that had permission from the authorities to hold a rally in the city on Saturday, so why would we shoot out own supporters?"
Extortion and gangsterism
He says that the killings are the fault of the PPP, the Awami National Party and an alliance of Islamic parties who "wanted to politicise the issue of the chief justice's suspension".
"It is the death squads of these parties who were responsible for the carnage, and nothing to do with MQM," he said.
Mr Hussain addresses thousands from London
Mr Anwar says that the MQM - which has 42 seats in the 168-member Sindh assembly and 19 members in the 342-member Pakistani National Assembly - is one of the few parties in Pakistan that believes in the rule of law and multiparty democracy.
"We are the last bastion against the Talebanisation of the country," he says.
Mr Anwar says that, even though Altaf Hussain has not been back to Pakistan for more than a decade, support for the MQM is growing - both in Sindh, where it is the main constituent of the governing coalition - and elsewhere in the country.
"We are not just supported by Mohajirs, but also have the backing of Punjabis, Sindhis, Balochs and Kashmiris," he says.
"Recently we have gained support in the province of Punjab and have even made in-roads in Pakistani-administered Kashmir."
The MQM denies its reputation for extortion and gangsterism in Karachi, and insists its main priority is to protect vulnerable people in the city and the rest of Sindh.
Mr Anwar says that the MQM's support for President Musharraf - a Mohajir - is not unconditional and that he must soon make a decision as to whether he can remain head of the army as well as president.
The office in London is largely staffed by volunteers
The party says that the president's efforts to remove the chief justice should be determined only by the Supreme Court.
On the subject of when - if ever - Mr Hussain will return to Pakistan and directly lead his growing band of supporters, Mr Anwar was more cagey.
"Altaf Hussain has frequently been warned by the security forces that if he goes back to Pakistan he will be targeted by mad mullahs and those who support jihad.
"If the president and the prime minister of Pakistan - both recently the subjects of assassination attempts - cannot be adequately protected, I'm not sure it would be sensible for him to go back.
"Anyway, in these days of high-tech communication why not govern Karachi from London? It's a new form of outsourcing."