The gang is believed to have dumped up to 100kg of heroin - worth pounds 20m - on to streets across the country every week.
It was brought in from Turkey and passed through what police described as a "clearing house" in north London before being distributed to smaller dealers.
After two raids on houses in north and east London, 14 men have been arrested and around pounds 5m of heroin recovered.
Detective Chief Inspector John Shatford, heading the operation, said the raids would severely disrupt the flow of heroin in to the UK. "We believe that all the heroin coming into this country goes to this gang in north London which acts as a clearing house," he said. "It is difficult to imagine a more significant seizure and we are all very pleased."
A spokeswoman for Scotland Yard said the year-long operation to track down the rest of the gang, which includes a number of Turkish nationals who used the local Turkish community as a cover for their activities, would continue.Reuse content