They don't want you just to be afraid of getting on a plane, train, tube, bus etc....they want you to be afraid wherever you are....they want to ruin our lives by injecting fear of both the random and organised attack. Uncertainty and instability are their goals. The war on terrorism is being won by radical islamists, not because of their military might, but because we're the ones who are terrified.
Gonna need a bit more than that to truly terrify most Londoners - i.e. the response after 7/7 most got straight back on with it determined not to be scared by it.