The discovery of 105 white and black rhino horns worth pounds 2.8m in crates in lock-up mews garages in Kensington followed a joint undercover operation between officers from the South East Regional Crime Squad and the Royal Society for the Prevention of Cruelty Against Animals. An RSPCA official described the discovery as "absolutely fantastic".
Two men and two women, all from the Cambridge area, were arrested as part of Operation Morello, shortly after 2pm yesterday. One of the women was released without charge last night.
Experts believe the horns are from rhinos in Southern Africa, though many of them may have been stockpiled over a period of more than a year.
It is thought that London was being used as a staging post for the horns - with the market likely to be the Far East and Middle East. The largest horn was valued at pounds 96,000.
The RSPCA's chief inspector, Terry Spamer, said: "The white rhinos we found today represent more than 1 per cent of the entire world population of white rhinos and there is enormous cruelty involved in the poaching of these animals. This would have flooded the UK market."
Roy Clark, regional coordinator of the South East Regional Crime Squad, added: "This is an excellent example of good co-operation between agencies."
A spokeswoman for the Worldwide Fund for Nature (WWF) - which has recently had two of the rhinos that it supports killed by poachers - said: "This is obviously a breakthrough in the fight against the illegal trade in wildlife which threatens many species, including the rhinos, with extinction."
In addition to its use as a supposed aphrodisiac, ground rhino horn is used in many Chinese communities for medicinal purposes. The horns are also valued as dagger handles in Middle East countries like Yemen where they are known as jambiyyas.
According to the WWF, the black rhinoceros population has dropped to just over 2,400, with most of those that remain being found in South Africa, Namibia, Kenya and Zimbabwe. The white rhinoceros population is estimated at about 7,500 - with the vast majority in South Africa.
In recent years, the populations of both species have existed in mostly protected areas, leading to speculation that the current haul comes from previously poached stocks or even old trophies that may have languished on game hunters' walls for years.
A spokesman for the Convention on the International Trade in Endangered Species (Cites) said it was studying the development.
A spokesman for the Department of Environment said the discovery was a good example of cross-agency partnership and added that the United Kingdom was committed to the protection of endangered species under the international convention.
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