I am always completely gobsmacked at how the cabin baggage policy is NOT enforced. You would think that this was one of the fundamentals of boarding requirements... to check that all cabin bags meet the maximum size limits.
On my last flight from DXB to LHR there were two people with very (and I mean) very large rucksacks with sleeping bags and who knows what else hanging on the outside. It was bigger than my 32kg case I use when going to the USA... and yes, they allowed it as hand baggage! Ridiculous!
I do wish BA would actually enforce the hand baggage limitations for all flights.