I can also suggest
Avoiding paying by card on wireless terminals in restaurant chains staffed entirely by minimum-wage temporary residents - which is pretty much all of them. But also avoid carrying cash because pick-pockets operate in tube stations.
Basically, avoid London.
What bewilders me are those pathetic little clear green plastic inserts with a tilt-view lenticular picture of a padlock (not even a proper hologram) that some ATM providers fit over the card slot 'for security'. They just look for all the world like some dodgy card skimmer bought for a few quid off a Hong Kong eBay seller and super-glued on by some chav at two in the morning.