A sniffer dog at Manchester Airport helped Border Force officers find at least 50 kilos of heroin, worth about £5m, hidden inside a shipment of carpets.
The seizure was made In April when officers became suspicious of a 46-piece consignment of hand-made knotted carpets that had arrived from Peshawar in Pakistan via Abu Dhabi.
A detector dog alerted its handler to one of the carpets and further examination revealed a "highly sophisticated" concealment where the drug was woven into the fabric of the carpet, a Border Force spokesman said.
It is thought that the total value of the drugs could run into millions of pounds.
Two people were arrested on suspicion of drug importation offences at a business address in London on April 29.
The pair were interviewed by NCA investigators and released on bail pending further enquiries.