Much depends upon whether you are going to sell up and sail and cut all ties with the UK or return to the UK on a regular basis. Most (but not all) of us in the Med are actually doing the latter, but our round-the-world friends are more likely to have cut all ties.
Strictly speaking, your doctor should take you off his/her list if you are out of the country for more than 3 months. However, if you are back in the UK several times a year and still have an address you are unlikely to have a problem.
If you take a regular prescription-only drug the cheapest way is to get your supplies in this country and take them out with you. Most doctors will issue a three-month prescription and will allow you to apply for a repeat by post.
Many drugs that are prescription-only in the UK are over-the-counter in Europe but I would only advise buying ones that have previously been prescibed for you back home.