Specialist sniffer dogs detected the drugs which were expertly disguised inside thread-like sheathes that look like carpet yarn to the naked eye, the Telegraph reports.
Two men, aged 35 and 51 were arrested after 110lb (50kg) of the Class A drug was found in the consignment that arrived from Peshawar via Abu Dhabi.
The seizure was made after Border Force officers became suspicious of the 46-piece consignment of handmade rugs.
Border Force officers and the National Crime Agency's (NCA) Border Policing Command made the seizure and the arrests in April. Examination of the load continues and officers say the drugs haul could increase.
The pair were held on suspicion of drug importation at a business premises in London and have been released on bail, according to the BBC.
Pete Avery, from the NCA's Border Policing Command, said: "It was a sophisticated concealment and demonstrates the lengths organised crime groups go to in an effort to avoid detection."
Linda Paul, assistant director for Border Force, added: "At this stage it is impossible to put an exact value on the drugs because forensic tests have yet to be carried out."
According to the Telegraph, the haul is already among the largest drug seizures made at Manchester Airport.