Detectives swooped on an address in Dublin following a month-long investigation by a joint Scotland Yard and gardai team after three warning letters were sent to senior figures, including Tony Blair.
The threat last month to conduct a "campaign of chemical warfare" by contaminating water supplies in England purported to come from a previously unknown terror organisation, the Republican Revenge Group.
The man arrested, described by police as a maverick Irish republican, was detained under the Irish Republic's anti-terrorist legislation by the National Bureau of Criminal Investigation. Irish police confirmed the man, in his fifties, was held under section 30 of the Offences Against the State Act at Mountjoy station in the north of the capital.
The threatening letters, sent to Luciano Storero, the papal nuncio (representative), and Ivor Roberts, the British ambassador in Dublin, as well as the water industry regulator, Ofwat, in Birmingham, demanded a commitment to a "total British military and political withdrawal" from Northern Ireland by 16 June. A detailed document, outlining how the mass poisoning would be carried out, was with the letters.
A news blackout was imposed in Britain and the Irish Republic as the operation began to track down the blackmailer. An urgent assessment by water industry and toxicology experts established that the method outlined in the letters would not pose a threat to public health, the Cabinet Office said last night.Reuse content