For VHF: Kisdon G/NP-026 - it is surrounded by higher fells. Similarly, Burton Hill G/WB-020 was tricky with its wooded summit area. Hensbarrow Beacon G/DC-004 was impossible on VHF being shielded from civilisation by a ten metre wall of landfill! While Carnmenellis G/DC-007 has a neighbour who called the police on us…
While a 2-pointer, Divis GI/AH-004 is of English 1-pointer height. The access road is not really on for approach because you just would not risk parking your car at the start of it, a run-down estate in Belfast. So a long boggy moorland trackless plod is required, and the breakthrough from the radars on the summit is the most extreme I have ever experienced.
Mynydd Enlli GW/NW-072 has the challenge of whether the boat is running on that day/in that weather, and then the challenge of being able to afford it! But this is all out of context; I presume Roger’s original question refers to the nature of the actual physical ascent. In this respect, I nominate the following beasts:
GW/NW-067 Moel-y-gest - OK, not really hard, but a fair amount of ascent to do and the route is not straightforward, especially not at the end of a long tiring day!
GW/NW-056 Moel y Dyniewydd - start near sea level, end near the upper reaches of the one point band. Not done it since Liam was just turned 6, so would probably find it easier now.
GW/MW-027 Moel y Golfa - steep, and just keeps going up and up!
G/WB-006 Caer Caradoc Hill - steep and requires a real effort on the ascent. Lovely hill though, and doesn’t actually take that long.
I am sure there are many considerably more difficult one-pointers in Scotland!