Mervyn Jones, the Chief Constable of Cheshire, whose force dealt with the Wilmslow incident, said he was "amazed" at the new tactic, and the anti-terrorist branch at Scotland Yard were left scratching their heads about the Provos' action.
The use of code-words is essential to the police if they are to save lives before a bomb explodes. But officers need to be sure the codes come from "genuine" terrorists, rather than cranks and time-wasters.
The procedure for organising codes has been long established. Codes alter periodically by agreement between the Provisionals and the security forces, both sides knowing that a failure in communications could be catastrophic. The IRA pass on a chosen name to the Gardai in Dublin, who in turn give it to the RUC Special Branch in Belfast. From there it is disseminated to forces on the mainland. Liaison is also held with a number of news organisations.
In Northern Ireland, however, the complication is that the IRA are not the only bombers. Because of the number of factions, up to six code-names could be in use at a given time.
None of the paramilitaries who wants to establish a bomb code is turned away. But this policy can sometimes lead to almost surreal problems. One detective recalled: "A few years back, a fairly obscure Protestant group phoned up with a bomb warning code-name. They kept updating it and each one got more sectarian. Finally they came up with 'F--- the Pope', until the officer dealing with them pointed out that, with Catholic officers in the service, a code-name like that was 'more likely to lead to an explosion than prevent one'."
Terrorism expert Professor Paul Wilkinson said that while the system was an essential safeguard. "It's like when terrorists warn about police about a bomb so they can clear the area,"he said. "Sometimes it's nothing like enough time - but you have to be grateful for any warning at all."