Hi Ron,
On the RSGB calculator it shows 2 results. On using 1998 limits & one showing 2020 limits.
The 1998 limits seem far more conservative. That was where I was getting 8m from.
The 2020 are more relaxed/sensible.
With the antenna at 6m above ground, I reckon I’m good for 400w, or up to 600w if I really want to (when our limit changes to 1000w).
So yes, the 1998 limits are probably significantly more conservative than the VK limits.