Nope, it's true. When I went for the first time a couple of years ago, my bank decided I needed more £50 notes than anything, and I got several "Wow, it's been a while since I've seen one of these," comments when I used them.
Also, fwiw, depending on where you're heading in the UK, cashless payments can be way more prevalent than they are in many places. I've been to multiple bars in and around Manchester that just didn't accept cash, and would bring out a card terminal to tap for every £2-3 beer I ordered.
On the other hand, bring a coin purse or something with you, because when you do use cash, you'll get a ton of coins back, and it becomes a pain to have rattling about in your pocket real quick.
A therapist probably wouldn't hurt to give a try.
You could also take stock of sources of stress in your life, especially any that have emerged/increased in intensity in the last few months. At my previous job, my anxiety took a massive spike due to a crazy boss, layoffs hanging over everyone's heads and an increasing workload. Even on anxiety meds, I was getting massive headaches on a daily basis and would spend hours on the verge of being ill from it. Once I got laid off, the anxiety went back down to my more manageable baseline, and the medication became a lot more effective for managing it.
Obviously, just entirely leaving the situation isn't a great option for everyone (heck, I lost the best paid job I ever had in the process, which wasn't great), but even if that isn't feasible, it might give you some insight into how you might mitigate the issue.
Also, keep on going when treatments don't work. There's no magic bullet here that works for everyone, so while it can be frustrating, keep trying things until you land on something that does the trick for you.