They allow you to jump any queue by simply saying the words "I'm a Silver card holder you know" as long as they are clearly visible on your bag. Go on, try it...

More seriously, they do nothing most of the time. On checked luggage I have been convinced in the past it HAS helped (same class, same check-in desk/time, my bag comes out significantly faster than my colleague's) but that seems to be at outstations. At LON, expect the bloody-minded work-to-rule baggage mishandlers to chuck your case out last.

Now I'm sure this will spark the debate about having them a danglin' from your hand luggage yet again so I may as well get in there...yes, I do it. Why? Because in the past it has resulted in being plucked from queues by eagle-eyed BA staffers and just for the few times that's relevant or happened, they've been worth their weight in, err, Gold On the flipside, there's the camp who find it terribly gauche and wouldn't dream of it. FWIW, I ensure they're only on when I am actually flying - I do chuckle at the people with Silver tags dangling from their rucksack on their morning Tube commute when they won't be going anywhere near an airport [how do I know they aren't just going on a nice ex-EU B2B later that day? Unless they do it every day...].