As you are fully aware, there is no state of emergency in the UK.
You do not know the reasons behind the holding of these pax and nor do I. I can guess as to the reasons behind it, based on my previous experience. But at the end of the day I can only guess. The difference is, I am basing that guess on experience, not gut reaction to half a story.
The majority were undoubtadly innocent (if not all) but in order to establish that, everyone gets held. Its tough but its life. Same would apply if you were at a party raided for drugs, you wouldn't be leaving until you had been cleared. So this is nothing new. If you don't like it, then don't fly. If you do fly, then accept it as one of the hazards.
Complain to your MP if that makes you feel better, it will be investigated and it will waste a large amount of money (the paperwork and time involved is huge in complaints against police) which could be better employed fighting crime, but then its your money paid out in taxes so think about how you'd like it spent.....You'd be better complaining to the airlines, its thier responsibility to feed you, not the Police.
Resouces? Has really got nothing to do with what the airport spends on security. I have done exactly the same thing at Heathrow, (only it was a 747 full of pax) the problem had nothing to do with the airport and its security.