Unusual for NTs to be 20 fret, as advantage is taken of the inherent ability to access higher frets with 24 frets being pretty much the norm. Is it a deal breaker?
I'm very happy with my Jim Reed BE5 (pic in my avatar), an Italian make that should fall well under your £800 budget, yet is good quality and ticks your other boxes. The mahogany body with birdseye koa top and back is pretty and the joins flawless, very smooth and fast-feeling neck. The pickups are Kramer-sourced and I keep thinking I'll replace them, yet the whole warm woodiness keeps changing my mind (2 band eq).
Not exactly easy to try before you buy, but I haven't regretted buying mine.
5-string club #568