Could those London bomb-makers actually do the deed or were they dupes like the "Miami terrorists" who had to be told what the target would be?
This very interesting article from Lew Rockwell addresses the unlikelyhood of this happening by addressing how the explosives would have to mixed while in flight to create an explosive misture.The bombers were supposedly going to use TATP, or triacetone triperoxide, a most delicate type of explosive.
Once again the government conspires to create terrorists where no terrorists exist???
Published stories after the arrests had references to the Bojinka Bomb Plot in 1994 which killed a Japanese business man aboard a Phillipines Airline.
It also interesting about the supposed plot to "blow up" an airline as the article relates to the Hawaii Airlines flight where the cabin roof blew off to due to major structural failure and still managed to land.
The Bojinka bomb (totally different from the TATP bombs)
The "Mark II" "microbombs" had Casio digital watches as the timers, stabilizers that looked like cotton wool balls, and an undetectable nitroglycerin as the explosive. Other ingredients included glycerin, nitrate, sulfuric acid, and minute concentrations of nitrobenzene, silver azide (silver trinitride), and liquid acetone. Two 9-volt batteries in each bomb were used as a power source. The batteries would be connected to light bulb filaments that would detonate the bomb. Murad and Yousef wired an SCR as the switch to trigger the filaments to detonate the bomb. There was an external socket hidden when the wires were pushed under the watch base as the bomber would wear it. The alteration was so small that the watch could still be worn in a normal manner.   
Yousef got batteries past airport security during his December 11 test bombing of Philippine Airlines Flight 434 by hiding them in hollowed-out heels of his shoes. Yousef smuggled the nitroglycerin on board by putting it inside a contact lens solution bottle.
The density of the explosive cocktail would be about 1.3.