British authorities confirmed on Tuesday that a Pakistan International Airlines (PIA) flight held over on Tuesday at Heathrow after a large quantity of heroin was found on board the aircraft.

Media reports confirmed that Border Force officers had found a "quantity of heroin" on board after the flight landed at Heathrow Airport on Monday.

According to Pakistan’s Dawn News, National Crime Agency officials said they were investigating the case but that no arrests had been made.

However, earlier in the day, an official said the flight crew had been detained after authorities found the drugs, reported Dawn adding that they had been released a few hours later.

Geo News meanwhile reported that the drugs had been distributed in bundles around different parts of the plane and that customs authorities in Pakistan have started an investigation into how the plane laden with heroin was provided clearance to fly.

The authorities have begun a probe against staff responsible for giving the clearance, reported Geo News.

The news channel also said that the PIA crew said customs authorities carried out a thorough search, going through each and everything, adding they had no clue as to why such treatment was meted out to them.