"uphill and down dale"
B Pier anyone? Or C Pier for that matter.
So true about someone entering a check in hall with a rucksack. How many of those are there every day?
It's all about preventing the last atrocity, never anticipating and preventing the next one.
Airports and aircraft are so relatively impenetrable now (i.e. the GLA bombers didn't even get all the way through the front door), that my money's on rail stations, shopping centres, schools, hospitals, Wembley, or anywhere else with minimal security measures.
Alternatively, sitting up in the Peak District under the arrivals track with a shoulder-launched missile, with a getaway vehicle waiting: that'd be an easy win for the terrorists, eh?
Be vigilant, everyone.