Heroin said to be worth more than £8.5m has been found stashed in boxes of fruit and nuts at Heathrow Airport.
Border Force officers found 170kg of the class A drug hidden in envelopes concealed in the walls of a consignment containing 630 boxes on 21 May.
Two men, aged 36 and 51, were arrested near Bradford on suspicion of importing class A drugs the following day, and a third was held in Birmingham on 23 May.
They have all been released under investigation.
The minister for immigration compliance and the courts said the seizure was the largest detected so far this year at Heathrow.
Chris Philp said: “Illegal drugs fuel crime, violence and exploitation which is why our work to prevent them reaching our communities is so vital.”