what are you looking for that you can't get in your NHS one Groom? IMHO the NHS ones now are fabulous, and you can pay £000's for a private one which won't help you hear any better (depending on why you need it of course)
I agree with bednobs --Nhs aids, are excellent servicing and batteries free as well.However if you are seeking something which looks cosmetically better ,then I fully understand.
I have had a hearing aid ,nhs, for 30 years and my only interest is being able to hear well. I don't worry about what it looks like , or if you can see it. As long as I can hear well --I don't see it-- others might and that is not my problem.
Best of luck with whatever you decide.