WWYD B ank passing counterfeit notes

I am absolutely feckin fuming. I went in to Yorkshire Bank today and withdrew a large amount of cash from my account and then went to a branch of Lloyds TSB just across the road to pay it in to a friend's account. When I was paying it in one of the £20 notes was refused by the teller as she said it was counterfeit. They confiscated it to send off to be tested (4-5 weeks before we'll get a reply) but gave me a photocopy etc to show to my bank. Now I wasn 't really expecting YB to say "here's your £20 back, sorry" but they were completely blase about the whole thing and said that we'd just have to wait until Lloyds got back in touch and if it was counterfeit then I'd be out of pocket as Yorkshire Bank wouldn't refund me that money. So basically they can mnake a *** up and accept counterfeit notes from someone but it's the next customer who's then out of pocket. I'm livid, I know it's only £20 (lucky it wasn't more) but it's the principle of the thing.