The incident happened yesterday when PK 785 from Islamabad to London arrived at the airport at 2:50pm.
Upon landing, as passengers disembarked, the flight crew and aircraft were searched by authorities, PIA spokesman Mashood Tajwar said.
The 14 crew members were kept in detention for five hours and, according to UK Border Agency (UKBA) sources, information had been received from Pakistan that there were narcotics on board the flight, Geo TV reported.
However, the National Crime Agency and UKBA agents, after searching the plane for approximately four hours, did not find anything.
The crew was later released after being questioned but their passports were withheld by the UKBA, which stated that further questioning might take place.
According to UKBA officials, the inquiry is still ongoing and after they are satisfied the next steps will be announced regarding whether the passports would be released or charges filed, the report said.
"We have not been informed as to why was the crew detained?" said Tajwar.
PIA has been suffering huge losses and administration is trying to improve the situation but the airline is frequently facing embarrassment.
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.
In February, a Heathrow-bound PIA aircraft was intercepted and escorted by fighter jets to Stansted Airport in northeast London because of a "vague security threat". Later, a suspect was arrested and charged with fraud and misrepresentation by Met Police.
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