British authorities confirmed Tuesday that their Border Force officers had found a "quantity of heroin" on board a Pakistan International Airlines (PIA) flight that landed at Heathrow Airport Monday.

The authorities further said National Crime Agency officials were investigating the case after the seizure of narcotics from the plane.

"No arrests have been made, enquiries are ongoing,” said an official associated with the agency, in an email response to Dawn.com.

Earlier in the day, PIA spokesperson Mashhood Tajwar had confirmed that British authorities had "thoroughly searched" and detained the flight crew after they landed at Heathrow Airport.

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Flight 785 from Islamabad to London had landed at 2:50pm Monday. Upon landing, as passengers disembarked, the flight crew and aircraft were searched by the authorities, the spokesperson said.

Fourteen crew members were released after being detained for nearly two hours by British authorities, Tajwar added.

"We have not been informed as to why was the crew detained," Tajwar had initially said, adding that the flight had since returned to Pakistan at 11:30 am Tuesday.

Commenting on the drug bust, he said that PIA had not been informed in writing or verbally about any such development.

"Our operations in the UK are running smoothly and every thing is fine," he added.

The national carrier often comes under fire for poor performance, low safety standards and the unprofessional attitude of its staff.

Members of PIA crew have also been sacked for smuggling contraband and assisting money laundering operations.

In January, as many as seven passengers were forced to stand throughout the over three-hour flight from Karachi to Madina after the airline boarded excess passengers in a serious breach of air safety regulations.

More recently, PIA came under fire when it emerged that a senior pilot operating the Islamabad to London flight handed over the aircraft to an under-training pilot soon after the take-off and took a two-and-a-half-hour nap in the passenger compartment, compromising air safety and putting the lives of over 305 passengers at risk.

The airline has taken a firm stance against corrupt practices and recently announced “termination from service” will now be the only punishment if any staffer of PIA is involved in smuggling contraband in or out of the country.