Would it have worked?
I have neglected to comment on the alleged terrorist plot to blow up airplanes in mid air because, to date, there is very little information available. I can't appraise whether they arrested people who appear to be terrorists of not. Certainly none of the "cellphone terrorists" in the US panned out to be what they were first alleged. So I'm waiting for the British to actually supply what amounts to evidence on which I can make an educated guess. But it does seems that there is reason to suspect whether the methods employed to blow up the plane would work or not. The alleged plot involved bringing aboard benign chemicals independently and they mixing them on board to produce the explosion.
One web site has looked into that. They write: "We're told that the suspects were planning to use TATP, or triacetone triperoxide, a high explosive that supposedly can be made from common household chemicals unlikely to be caught by airport screeners." Simple? Not really. They discuss the actual process needed for this to work:
First, you've got to get adequately concentrated hydrogen peroxide. This is hard to come by, so a large quantity of the three per cent solution sold in pharmacies might have to be concentrated by boiling off the water. Only this is risky, and can lead to mission failure by means of burning down your makeshift lab before a single infidel has been harmed.
But let's assume that you can obtain it in the required concentration, or cook it from a dilute solution without ruining your operation. Fine. The remaining ingredients, acetone and sulfuric acid, are far easier to obtain, and we can assume that you've got them on hand.
Now for the fun part. Take your hydrogen peroxide, acetone, and sulfuric acid, measure them very carefully, and put them into drinks bottles for convenient smuggling onto a plane. It's all right to mix the peroxide and acetone in one container, so long as it remains cool. Don't forget to bring several frozen gel-packs (preferably in a Styrofoam chiller deceptively marked "perishable foods"), a thermometer, a large beaker, a stirring rod, and a medicine dropper. You're going to need them.
It's best to fly first class and order Champagne. The bucket full of ice water, which the airline ought to supply, might possibly be adequate - especially if you have those cold gel-packs handy to supplement the ice, and the Styrofoam chiller handy for insulation - to get you through the cookery without starting a fire in the lavvie.
Easy does it
Once the plane is over the ocean, very discreetly bring all of your gear into the toilet. You might need to make several trips to avoid drawing attention. Once your kit is in place, put a beaker containing the peroxide / acetone mixture into the ice water bath (Champagne bucket), and start adding the acid, drop by drop, while stirring constantly. Watch the reaction temperature carefully. The mixture will heat, and if it gets too hot, you'll end up with a weak explosive. In fact, if it gets really hot, you'll get a premature explosion possibly sufficient to kill you, but probably no one else.
After a few hours - assuming, by some miracle, that the fumes haven't overcome you or alerted passengers or the flight crew to your activities - you'll have a quantity of TATP with which to carry out your mission. Now all you need to do is dry it for an hour or two.The genius of this scheme is that TATP is relatively easy to detonate. But you must make enough of it to crash the plane, and you must make it with care to assure potency. One needs quality stuff to commit "mass murder on an unimaginable scale," as Deputy Police Commissioner Paul Stephenson put it.
The full article goes into much more detail and is worth reading. So provided the alleged terrorists were not so alleged but legitimate, and assuming they actually planned to do what we have been told they were going to do, the implication seems to be that the plan wouldn't have worked.