Hussain, London-based the founder of the MQM, resigned as chief of the party early today to protest Scotland Yard's raid at his house in the UK.
Following his announcement, hundreds of MQM workers gathered at Nine Zero in Karachi's Azizabad area, requesting the MQM leader to take back his resignation.
The party also announced that its workers would stage a sit-in in front of the British High Commission to protest against what the MQM chief called as a conspiracy hatched against him by the British government to unnecessarily drag him in the investigation of Imran Farooq's murder.
British police raided two homes of in north-west London in connection with the brutal murder of Farooq on June 18.
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Speaking to media via telephone from UK, Hussain said Scotland Yard police had raided his residence some days ago and had seized some material, following which he decided to voluntarily step down as party leader on moral grounds.
Hussain said he would not seek legal counsel or a solicitor but would plead his case himself if he were to be produced in court in the Imran Farooq murder case. He said that he would accept any decision by the courts.