London is crazy though. If the most minuscule thing is wrong about your luggage they'll pass it through every security check.

Yep. The last few times I've been through London they've insisted on absolutely emptying my backpack because, and I quote, I had "carefully coiled cables in it". I'm an IT guy, I travel with a laptop, several devices for entertainment on a plane, chargers, etc. I promised them that next time I would toss the cables in haphazardly so as to prevent further issues. They were...unamused.

And god forbid you had a drop of liquid inside, as they will swab every nook and cranny of you bag and put the samples through some kind of detector.