As far as I am aware there is no state of war, nor has there ever been between the IRA and the UK. Yes there were threats to Heathrow before the mortar attacks, in fact they used to avarge 2 or 3 a day, mostly from nutters, sometimes from Terroist groups, were they fake? Speaking as someone who worked there as a policeman at the time, I think I am in a better position to judge. Irresective of that, yes threats can cause panic and or disruption. You have pointed out that the effect of sept 11th wasn't that great in compasion to the number of passengers carried etc. Correct it wasn't, but the impact of a all the threats made can cause equal if not more problems for all concerned, for instance the loss of revenue. Its therefore easy to see why terrorists (which includes the IRA) use threats as a weapon.
As regards to Lochabie, the informationwas somewhat more specific than you imply.
Having said that, and disregarding your incacuracies concerning history, some of what you suggest does make sense, sadly I think we can all rest assured the chances of your ideas being used are low.