The drug was discovered inside a suitcase near South Harrow Tube station by officers from the Middle Market Drugs Project (MMDP) on Sunday evening.

A 21-year-old man has been arrested in connection with the seizure.

It is the biggest seizure for the MMDP which was set up last November to stop organised criminals distributing Class A drugs in London.

Det Supt Steve Dann, MMDP head, said: "Drug dealers who target communities with Class A drugs like heroin create a problem which extends to many other crimes, with addicts stealing in order to fuel their habit.

"Clearly this operation has prevented a substantial amount of heroin reaching the streets of London."

The project consists of officers from the Met, Customs, City of London Police and the National Criminal Intelligence Service.