So, you should try NHS first -it’s free and you are British.
How and What you get does vary from region to region.
From what I can determine, the main differences are:
TECHNICAL: Thin tube hearing aids are widely distributed via the NHS, whereas thin wire (RIC) aids are often smaller and more efficient. A very few areas do offer thin wire hearing aids.
TECHNICAL: In some CCGs, there is a poor selection of dome sizes, and thin tube replacements, but not all.
TECHNICAL: The models used in the NHS MAY be less successful versions, already tried in the European market.
AESTHETIC: Thin wire hearing aids are smaller than thin tube.
HOLISTIC: A good private dispenser should spend much more time with you, with fine-tuning.