How a high-speed ocean chase led to an £18m cocaine seizure in Cornwall

Operation also shed unique light on backgrounds of those involved in running drugs into UK from mother ships'

• Public urged to help catch gangs bringing drugs on mother ships' to UK coast

To the surfers and dog walkers on the Cornish beach it must have looked like a scene from a crime thriller. An ocean chase ending with two boats crunching aground on the sand, a stumbling attempt by three men to escape into the dunes, dramatic arrests and the discovery of millions of pounds of cocaine.

For the investigators it was the start of a painstaking investigation that has shone a unique light into a tactic used by South American drug gangs and British organised crime groups known as at-sea drop-offs or Asdos, in which bales of cocaine fitted with GPS trackers are dumped at sea from a transatlantic mother" ships to be picked up by small vessels and smuggled into the UK via quiet coves and harbours.