The police were sorry for shooting a Brazilian and that wasn't as far as it went. Endangering persons on board an aircraft is an offence whether you meant to or not, as a passenger you only have to argue who endangered you the most. The person who wrote the note is an IDIOT, the person who found it did what they must - take it seriously. The Capt informs ATC and hopefully tells them HIS/HER intentions.
ATC have their procedures with regard to who to advise. Now this is what we're guessing about; the details go up the chain of command probably to the top, they look at the info 1. Paris--- shoe bomber---bad 2. Ireland--- used to be bad --bad 3. note----specific threat---bad
Already too many bads, so lets play it by the book- instigate the plan
back down the chain of command right the way back to the controller - instigate the plan; great idea, what plan? never mind I'll deal with it.
ACC; TC got a paddy with a bomb where do you want him for STN
TC; hes not going north of LHR it'll screw up my outbounds for the Ocean, not going south about coz Gordon B is coming thru DVR on a Kittyhawk. Can't go over the top?
ACC; no, don't worry he can go dct TRN to PIK.
Now back to reality, this was a very real bomb threat but the actions taken up the chain of command were for a very real unlawful interference event, that is the mistake. As usual, the contingency plans must have been written but putting them into practice fell short of the required standard. I wish the Captain had declared his intention to divert and followed it thru with or without a clearance, I hope he would not have been shot down but I wouldn't bet on it.