Where I live there is a field to the rear of me. It would give me the
distance I want from other people.
Its farmland and I know it cant be changed - besides there is an old mine
shaft in the middle of it.

Its not up for sale, but I was wondering if it is possible to approach the
owner to sell it. The owner doesn't use it at all. Ive lived at the rear
of
this field for 7 years and all he does with it is let the grass grow and
cuts it in the summer.

I wonder if, rather than buying it, you might be able to ask if he will
simply let you use the land. If not that then whether he'll rent you the
land. Buying it might be tricky - apart from the cost (he holds all the
cards), if it is farmland, converting it to domestic use will probably
involve getting planning permission too. An informal agreement between the
two of you might simply be easier.

However, I'd start by getting some plans of the area and finding out who
actually owns it (ie visiting the council). It sounds suspicious to me that
he maintains it but doesn't do anything with it. Are you sure he owns it?
What permissions does the land have? Maybe he can't use it for keeping
livestock/growing crops, for some reason.

Just my thoughts on this