Detectives seized 169kg of cocaine, with a street value of pounds 12m, at a house in Ostend, Belgium, which was thought to have been destined for Britain.
Graham Piper was arrested yesterday at his home in Wendover, Buckinghamshire, where he and his wife own a number of racehorses including the highly rated Nipper Reed.
Detectives spent yesterday searching their farm for documents and papers.
The raid was part of an international two-year inquiry codenamed Operation Pierrot. Police believe the operation, organised by the National Crime Squad (NCS), has broken up one of Britain's biggest drug gangs.
"The operation has dismantled what had been identified by the National Criminal Intelligence Service as one of the major drug trafficking organisations within the UK and will hopefully lead to the confiscation of assets in excess of pounds 3m," police said in a statement.
Detectives were investigating a number of suspected cocaine and cannabis smuggling networks that brought drugs into Britain from South America and Morocco via Europe.
As part of the inquiry six people were arrested on Sunday evening - although details were only released yesterday - at Heathrow airport and other locations throughout the South-east of England.
Five men and one woman were arrested and premises searched at Wendover; Runwell, Wickford and Clayhill, in Essex; and Bushey and Watford in Hertfordshire. The six were being questioned yesterday.
The eight-year-old Nipper Reed is considered a contender for the Arkle Challenge Trophy Chase at the Cheltenham Festival next month.
The raids followed the seizure of 169kg of cocaine in Ostend on Sunday by the Belgium gendamerie on behalf of the NCS. A Belgian man was arrested during the raid.
Four more people were arrested yesterday as part of the operation; a man and a woman after the discovery of cannabis plants and cocaine during the on-going search at a house in Runwell, Essex, and two menat Newcastle airport, where one is believed to have been waiting for the other to arrive from mainland Europe.
The operations also included work carried out by the NCS and Customs and Excise.
Detective Chief Inspector Peter Spindler, of the NCS, said: "The success results from the work of our highly professional staff, and from close co-operation with law enforcement colleagues in this country and in Europe."
A spokesman added: "This is the largest single cocaine seizure by the NCS since its inception in April last year."
John Abbott, director- general of the criminal intelligence service, said: "The operation was an excellent example of intelligence-led policing reaping major dividends. Substantial tactical intelligence from NCIS,with the operational capabilities of our partner organisations, resulted in the seizure of a huge quantity of drugs."Reuse content