Okay, I'm a little confused on this. Having lived in the UK for 8 years, I've had no trouble just getting money out of my local cash machine. It takes Plus and all the other familiar names, and their exchange rate goes up and down depending on the market for the day. Barclays doesn't charge for using their ATMs, though my bank in Hawaii charges me 3 bucks a pop, so I make sure to take out a fairly large amount each transaction. I then pay in cash, since I don't have an account here.
I also use my AmEx at Sainsburies regularly, though they have their own charges for using their card, the bastards. But the supermarkets and stores I've gone to almost all take Mastercard and Visa as well. In fact, it's really surprising to me that you're having trouble with this.
Am I missing something???
PS- If your bank won't give you checks, they can certainly set up a Direct Debit account for your bills to be paid through.
Also, my friend has his bank send him funds through a bank check and I don't think he pays a really high exchange for doing it. And he can put that directly into his English account to draw from as needed.
Does ANY of this help???