Just to clarify a bit.
Resolutions are :-
5m UK - = 1 pixel for every ~5meters of floor space. ( Disk space = ~ 4.62GB at roughly £20.00 depending on final pricing from GM )
2.5m UK = would therefore take around 18.48GB 4 times the space & price etc.
so 1m is prolly way too much lol
25centimeters per COUNTY as in Merseyside, NOT COUNTRY. ( just to clarify this point )