Two Pakistani students arrested on unproven terror allegations in England earlier this year returned to Pakistan on Thursday, a British official said. This is the latest chapter in a case that has strained relations between the two countries.

British High Commission spokeswoman, Jennifer Wilkes, said the pair agreed to leave Britain voluntarily and landed in the eastern Pakistani city of Lahore after an overnight flight from Manchester. Wilkes would not name the returnees, but the state-run Associated Press of Pakistan identified them as Rizwan Sharif and Umar Farooq.

British authorities arrested 12 students, most of them Pakistanis, in dramatic daytime raids in April but did not produce enough evidence to back up any terror charges.

London has insisted on deporting most of the students anyway on national security grounds.

Including the latest pair, five have agreed to leave voluntarily. One student was released very soon after the arrests, and two others were released on grounds they were no longer a threat.

One of the 12 turned out not to be a foreign national so was not suspect to deportation and has been released, Wilkes said. Three others remain in custody and still face deportation.

The case has strained British-Pakistani relations and embarrassed Britain, where Prime Minister Gordon Brown asserted early on that police had disrupted “a very big terrorist plot.”

Families of some of the students demanded they be allowed to continue their studies in Britain since the charges were never proven.

The arrests were rushed in part because a top British counter-terrorism official inadvertently exposed details of the operation to a photographer outside the premier’s office.

Representatives of the recently returned students could not immediately be reached for comment.

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