Imran Farooq, 50, a founding member of the Muttahida Qaumi Movement (MQM) party, was stabbed and beaten to death in Edgware in northwest London as he returned home from work in September 2010.
Interior Minister Chaudhry Nisar Ali Khan said Pakistan would help the British police in a transparent investigation.
“We will ensure proper investigation without any prejudice, without any favour,” he told reporters.
“The suspects are in custody of the Frontier Corps in Quetta. We will bring them to Islamabad and assist the British police in the investigations,” the minister said.
Announcing the arrest last week of Khalid Shamim and Mohsin Ali, Pakistan termed it a breakthrough in the case.
British detectives said last May they want to question Ali and another man, Muhammad Kashif Khan Kamran, about the attack. Both were in Britain in the period leading up to it and left hours afterwards.
Farooq claimed asylum in Britain in 1999. He was wanted in Pakistan on scores of charges including torture and murder related to the MQM’s activities, but always claimed the accusations were politically motivated.
He was twice elected an MP in Pakistan, but went into hiding in 1992 when the government ordered a military crackdown against party activists in Karachi.