Three alleged animal rights activists, including two Britons, have been arrested on suspicion of conspiracy to blackmail.
A 50-year-old woman was detained in Croydon, South London, while a man and a woman, both aged 25, were held by police in Amsterdam, The Netherlands.
Sky's crime correspondent Martin Brunt said: "I am told this is a result of a very long-running investigation led by Scotland Yard but involving police forces across Europe.
"Scotland Yard will be looking for the extradition of those two individuals in Amsterdam."
Officers are searching the home in Croydon where the 50-year-old was arrested, and a business address in central London, while Dutch counterparts are searching a home and a business in Amsterdam.
More to follow...