By Barbara Plett
BBC News, Islamabad
The Pakistani cricketer turned politician, Imran Khan, is due in the UK to plan legal action against another Pakistani politician, Altaf Hussein.
Imran Khan may be able to use new anti-terrorism laws in the UK
Mr Hussein lives in England but he heads a Pakistani party called the MQM.
The party was accused of using violence to stop the country's chief justice from visiting Karachi last month.
The judge's suspension by Pakistani leader and MQM ally, Gen Pervez Musharraf, has inspired an anti-government movement.
Imran Khan says he is collecting evidence to file against Mr Hussein in the British courts.
He says Mr Hussein makes all the key decisions in the MQM party, so it is he who must be held to account for recent violence in Karachi that has been widely blamed on his party.
'Recipe for violence'
The party denies it instigated gun battles that killed more than 40 people last month - but it has a history of militancy and street fighting.
Mr Hussein fled to London in the early 1990s during an army crackdown on the MQM.
He won asylum and then citizenship and has since directed the party from exile.
It is not clear on what legal grounds Mr Khan will build his case, but recent anti-terrorism legislation allows prosecution of British citizens who organise or incite violence abroad.
The Karachi street fights were related to the suspension of Pakistan's Chief Justice Iftikhar Mohammed Chaudhry and the anti-government movement that that has inspired.
He was visiting the city and his supporters planned a rally to welcome him.
The MQM, which is part of Gen Musharraf's ruling coalition, organised a counter-rally.
Observers said this was intended to prevent the opposition from putting on a show of strength and was a recipe for violence.