Awesome, it's good to know that Market Harborough has been sorted - it's always been a bit iffy there. Has the Orange mast at the train station (code 23433, still on HSPA, no DC-HSPA+) been done yet or is it still Orange and slow?
Update in regards to Sheringham (I'll do it on this post):
Bottom end of Sheringham (where most of the shops are): 1 bar 3G outdoors. Likely not very good indoors, but I didn't check.
By the train station: hopeless. Emergency Calls Only. May have been EDGE (there was EDGE down the high street, but there was also 3G there) but I didn't test as I'm more interested in a reliable data connection that works, rather than an old, slow 150kbps connection that won't work with most things (or will be painfully slow).
There was no Orange 3G, or even 2G, down the high street so the Orange mast may have been decommissioned (or may be doing the 3G on EE code, I don't know and didn't have the time for mast hunting!).
Weybourne was much better. Used to be very strong Orange 2G due to a nearby mast. Now EE 2G/3G/4G. Yes!

High Kelling (these are all places on the North Norfolk Railway, by the way): Variable. Some places, 10% (-107dBm?) 3G. Other places, nothing. Didn't test for 2G (due to the same reasons as above) but from previous years, when I was using an old Galaxy Ace Plus, on auto mode, it flicked between weak 3G, weak 2G, or nothing. I doubt 2G would have been reliable either, considering the surrounding terrain.
Which brings me on to the A148 (the road that links Cromer to King's Lynn). Quite hit-and-miss in regards to phone signals, sometimes more miss than hit!
Notable weak/deadspots on EE:
1) Certain areas between Cromer and Kelling Heath (including Kelling Heath)
2) Outskirts of Holt to Letheringsett
3) Passing through Little Snoring
4) East Rudham (possibly some areas in West Rudham too) - there but very weak, clinging onto -111/-113dBm! Not good...
5) Something that can only be classed as "The Hillington Disaster". Close to Hillington, Norfolk. It's a trisector mast but might as well only be a single sector mast with one panel! I'm not going to describe it in words, as this Google Maps image really does describe the problem for you: (note that the mast has been upgraded to EE 2G/3G/4G and 3 3G, with new panels, but that will not help one bit)
https://www.google.co.uk/maps/@52.80...7i13312!8i6656
Even 800MHz 4G at full power will not work there!
O2 have a mast nearby,
used to be a pitchfork 900MHz only mast, but is now CTIL and 2G/3G/4G 900/900/800.
I hope someone can sort out the location of that EE mast, which can only be described as a disaster. (Literally, after a couple of hundred meters from the EE mast, it went from a full 3G signal straight to No Service. I wonder why....)