UK Border Agency (UKBA) officers only discovered the drugs when they were alerted to an abandoned suitcase at Heathrow Airport on Friday.
On examining the bag, which arrived on a flight from Mexico, they found it contained 20 kilos of the class A drug.
The case was then passed to HM Revenue and Customs investigators.
Stuart Robinson, HMRC senior investigation officer, said: "At present we have not identified a passenger for this baggage.
"Our investigations in to this matter are ongoing."
Last month it was reported that the disruption of drug trafficking rings had caused the wholesale price of cocaine in Britain to rise by 15 per cent since last year, reflecting a fall in supply.
According to the Serious Organised Crime Agency, the smugglers who traffic the drug to Britain are "in retreat" following a series of operations against them.
Smuggling rings increasingly use West Africa as a staging post for bringing Latin American cocaine to Europe and Soca has responded by increasing its presence in the transit zone.