As I was paying for a couple of items at Cotswold Nottingham, the young lady at the till spotted my NT card in my wallet.

"Ah, you're a member of the National Trust."
"yes."
"Great, that means you get 15% off all full price items at Cotswold."
"Do I?"
"Yes, it's a tie-in we have, although I don't think the National Trust make much of it."

They certainly don't - or if they do, I missed it. So, if you're a NT member, remember to take your card with you the next time you're shopping at Cotswold and claim your 15% discount.

You can also get a discount from Mountain Warehouse for a CC or CC&C card, this applies to all purchases even heavily discounted sale items. And you don't have to spend anywhere as much on membership as the NT.

Cotswold Outdoor have quite a few affiliated discounts. It's worthwhile asking if making a purchase in-store and you have your club membership card on you. Examples include Camping & Caravan Club, NHS Staff, NUS, Armed Forces, Police, Ramblers, National Trust, Ski Club GB, YHA, etc etc.