British police have arrested self-exiled Pakistani politician Altaf Hussain as part of an investigation into his speeches made in 2016, according to media in Pakistan.Hussain, 65, is a leader of Muttahida Qaumi Movement (MQM), a political party with a large power base in the megacity of Karachi in the southern province of Sindh. He has been living in exile for more than 25 years.He was arrested in London on Tuesday in an early morning raid after a joint investigation with Pakistani authorities, broadcaster Geo News reported.Separately on Tuesday, the London Metropolitan Police said in a statement that a man in his 60s had been arrested "in connection with an investigation into a number of speeches made by an individual associated" with the MQM in Pakistan.The statement, however, did not identify the person arrested.It said the man "was arrested on suspicion of intentionally encouraging or assisting offences contrary to Section 44 of the Serious Crime Act 2007".Section 44 of the Serious Crimes Act states that a person has committed an offence if "he does an act capable of encouraging or assisting the commission of an offence and intends to encourage or assist its commission". MQM, which dominated Karachi in the 1980s and still enjoys a strong following in Pakistan's largest and wealthiest city, was splintered in two factions in 2016 after a series of anti-Pakistan and anti-military speeches made by him. Hussain's loyalists formed the London faction, while dissidents are based in Pakistan.Hussain sought asylum in the United Kingdom when security forces cracked down on the party in the 1990s.Even from exile in London, Hussain controlled Karachi through a powerful network. Pakistani police and his opponents have accused him of exhorting his supporters to violence, charges he has denied.The MQM, which claims to represent the Urdu-speaking migrants who moved to Pakistan with the partition of India in 1947, has often been accused of being involved in violence, with Hussain at the helm.His party is linked to a carnage in Karachi on May 12, 2007 which killed more than 50 people on the occasion of a lawyers rally to welcome then deposed Chief Justice of the Supreme Court Iftikhar Chaudhry.Hussain is also accused of masterminding the murder of his close aide and the party's former Secretary-General Imran Farooq, who was stabbed to death in 2010 in London.The party had managed to win majority seats in elections from Karachi from 1988 to 2013, however it conceded a huge blow in the 2018 elections at the hands of Prime Minister Imran Khan's Pakistan Tehreek-e-Insaf Party.Prime Minister Imran Khan came to power last year vowing to attack rampant political corruption in Pakistan and there have been a string of high profile cases.Opposition parties say the government is using corruption as a pretext to silence its opponents while it also cracks down on groups such the Pashtun Tahafuz Movement (PTM), an ethnic Pashtun rights group.Hussain's reported arrest in London followed other detentions of opposition politicians in Pakistan.On Monday, former President Asif Ali Zardari, leader of the opposition Pakistan Peoples Party (PPP), was arrested by the National Accountability Bureau (NAB) on corruption charges.Zardari spent 11 years in jail on corruption and murder charges before becoming president in 2008. But he was never convicted and denies wrongdoing.On Tuesday, Hamza Shahbaz, nephew of former Prime Minister Nawaz Sharif, was taken into custody on charges of money laundering and possessing assets beyond his means. He later told reporters he was not guilty.Sharif's Pakistan Muslim League-Nawaz party said the arrest was politically motivated and part of a campaign to target opposition parties.