Hier kun je discussieren over Smeris inval a'dam.
A woman, 50, was held in Croydon, south London, on suspicion of conspiracy to blackmail following her arrest by counter terrorism officers, police say.
A man and a woman, both aged 25, were also arrested at a residential address in the Netherlands.
Searches are ongoing at business addresses linked to all three.
BBC home affairs correspondent Danny Shaw said Scotland Yard was not revealing who or what the alleged target of the blackmail plot was, but it is understood it was in the UK.
Sources said the operation was one of the most significant that police tackling animal rights extremism have conducted for some time, he added.
It was led by the Metropolitan Police Service Counter Terrorism Command, in liaison with the National Domestic Extremism Unit and Dutch National Crime Squad.
http://www.bbc.co.uk/news/uk-18737381