Update:
Just been along the troublesome Eye Green/Eye stretch of the A47 that has troublesome coverage on EE (due to not being on the nearby CTIL mast or building other masts).
3G2100 weak as per normal. There, but very weak. In some areas of Eye there is no 3G2100.
4G1800 quite weak. Certainly not as weak as 3G2100 (I think it reported about 30-35%, so just under 1 bar) but certainly not ideal. Would work outdoors in Eye but not in Eye Green (likely too weak to be usable).
However...
Shoved it onto EDGE for a quick test of coverage and EDGE showed up to be about 35%. This is interesting as it is 2-3 bars of signal, so much better than the 0-1 bars on 3G or 4G.
Would certainly be usable outdoors and indoors in Eye, likely outdoors only in Eye Green. (Though of course, not for data, as EDGE is just terrible.)
So the future seems promising, even if EE don't build a new mast. Once the power is increased on 4G, to 2G levels, Eye will be fine for coverage, with Eye Green requiring 800MHz to work indoors. Not ideal as Vod/O2 have a CTIL mast nearby doing 2G900/3G900/4G800, possibly 3G2100, so CTIL is still the network to be on (unless EE build a new mast there), but much better than what I previously thought.
Assuming that 800 is launched in that area (which I thought would happen, because of the rural area and distance between masts) and the L1800 power-up to G1800 levels does happen, EE will be OK... just about.
edit: Three seem to have resolved the problem via rolling out 800MHz on the nearest mast... hopefully EE will do the same.