This remind me of the story about the guy on a cross-country train trip in Scotland who tore up a newspaper and tossed bits out the window every few miles. He was asked what he was doing and he replied that it was to keep the lions from attacking the train. The fact that the train was not attacked by lions proved he was right.
It will be hard to know, but from reports issued by BA etc there was no specific threat, and no terrorists were caught. In fact by publicising it the way they did, the bad guys would have merely delayed their attack, not cancelled it. I have never heard of a single case in the entire history of aviation where a threat to an airplane ever resulted in an attack (bombing, hijacking or whatever). Every attack has been a surprise, with no warning given. And we know that the terrorists are much smarter now; it is hard to see how they will be stopped by all this stupidity. Even the 'best' airline for security (El Al) saw an attempted hijacking last year, with one of the only cases of a real weapon (a pocket knife) being used.
Do we know that the current paranoid hysteria has any effect on preventing or deterring terrorists? Is there in fact any plan to attack airplanes, or are they merely stirring the pot to see the reaction? Or, more likely, is it being done by some govt department in order to cause panic and enable them to expand their control and influence? (making themselves more important and thus entitled to more money). If there is no attack after the paranoia dies down it will allow them to claim they stopped an attack, just like the guy with the newspaper.
Remember they still have not closed the loopholes at the airports; only crew and passengers have to go through security, all others come and go as they please.
Telling foreign cargo airlines that they have to carry air marshalls and have strengthened cockpit doors if they want to fly to the US is pure protectionism, and I wonder how much of all this garbage is meant to be more of the same.