Dear me! We love to ridicule journos for their dimness and lack of understanding but that doesn't prevent some of out members eclipsing that a hundredfold does it?
Surely, surely even dimmest amongst us can see that what that achieves is in the ultimate event it drops a pile of wreckage somewhere, anywhere, where it cannot do a thousandth of the damage that it would if plunged into the Olympic Stadium killing 50,000 or wiping out the House of Commons (I'll refrain from the witless sarcasm that is bound to follow that statement).
For those without a sense of proportion it is called "Damage Limitation" and given the threat it would be criminally irresponsible not to take such a precaution.
Arrant nonsense!
The facts are that these missiles are the last line of defence and as such will have failed to achieve any purpose whatsoever if used. A large passenger aircraft crashing, controlled or not, into the massive target which is London will cause catastrophic carnage regardless of any preposterous theory that shooting it down will somehow limit the damage. Besides, the inertia built in to the decision to shoot it down will guarantee that won't happen.