It's designed for duty free
I do whatever I can to stay the he11 away from BA, or any airline combination that transits through the UK because of their illogical, draconian, across-the-board 1 piece of carry-on luggage policy.
Nobody's ever explained why, in addition to a computer case or purse that can fit under one's seat, does a garment or small roll-on that can easily fit into overhead pose a "security threat"? (because if you question this policy you're informed it's "for your security, sir").
Why can someone board a BA flight in the US, checked-in by BA personnel, with a personal item and a carry-on and fly to the UK, but upon arriving can't transit out without checking one of them? What magically changes enroute?
More patronizing "it's for your security" answers is all you'll get. They act as if you should feel fortunate to be standing in one of their 90-minute quues..queues..qusu....lines.
Also, they seem to have to resources to hire an inordinate amount of employees who do nothing more than wander around the lines barking orders and chastizing those that make up their captive audience.
Yet, once you get past security with your 1 bag at LHR or LGW, there loom large signs advertising the fact that you can now carry on anything you buy in the duty-free shops onto the plane. So someone's duty-free perfume (or whatever) purchase poses no threat, but a bag containing a change of clothes that I'd love to have at my destination when the famously-bad baggage handlers in the UK lose my luggage does?
And anyone who's been in a security line knows that they're slow NOT due to people putting 2 bags on the conveyer to be x-rayed instead of 1, but waiting for people (who've been in line for 30 minutes) who wait until they're at the front of the line to decide to empty their pockets of phones, change, belt, etc. etc......as if the requirement to do so was sprung on them as a big suprise.
I'll take the occasional, surly US screener anyday to a policy that patronizingly treats you like a peasant one moment, then attempts to entice you to shop and carry-on whatever you buy from them the next.