I have been into Halfords in Huddersfield today and presented my Gold Card so he could attribute the discount but the lad said they don't do that, he had never seen one before and he thought I probably needed to download a voucher.
I persued my stance and eventually after he made a phone call and got help from a colleague, he applied the discount and on the receipt it says, Price Overide. Reason: Store manager authorised.
So, get ready to explain and demand the discount if shops are unaware!