This is where the big disconnect comes in understanding the true threat. Pilots nearly universally laugh at the idea of using light airplanes for a terrorist action. A light airplane has little chance of doing much damage, most say. However, those who believe this really do miss the big picture.
A light airplane gets used for a terrorist function. A few people die. A little damage is done. Fair enough.
However...overnight your flight schools shut down, and don't reopen. (in the US, after 09/11, a third of the flight schools in the country went out of business). General aviation comes to a near standstill. You can't even visit your own airplane again without a pass, and often an escort. You're fingerprinted a dozen times, the subject of multiple security clearances, and when you do go fly, you're intercepted in your PA-28 by a fighter that is prepared to shoot you down. IFR flight plans required for everything. The costs go up. Screening is in effect at your local airport. Medical flights, freight flights, traffic reporting, you name it...all severely curtailed, delayed, stopped, cancelled...and suddenly you're in the same position as the US.
The amount of damage done in the US following 09/11 was enormous. Not from the damage to the world trade center, though that was tragic. The real damage was the fear, the terror, and the economic impact particularly to general aviation. You see two or three light airplanes in the UK used for such an activity and it won't matter if a single soul is hurt or killed, or if a single pound, euro, or dollar is lost. The psychological damage, the publicity, the outcry will be enough that whatever limited flying you get to do now will be gone and probably won't be back.
The real threat is what comes afterward. For that reason alone, it's something that every single pilot should take very seriously. Very, very seriously. Act and watch accordingly, because it only takes once.