Height restrictions on model aircraft

We all know ( or should ) that there are restrictions on altitude based on aircraft weight. However, what I confess I'm not clear on is whether the quoted height limit is above sea level, or ground level where the pilot is. This could clearly have implications for slopers of certain models.
The Orme for example is 700 ft at the peak, and probably around 400 feet+ where we fly?
In summary, as I understand it, the limits are....
1) Under 7kg - no limit
2) 7-20 kg - 400 feet ( now including pure gliders since a few years ago )
3) 20kg+ errrr, that's not a model aeroplane anymore its a light aircraft and you'd better be familiar with ALL the CAA rules and regs, as well as LMA approval of model and pilot etc.

So, for 2)...... sea level or ground level? My assumption is sea level.

If you assume that it is above sea level Tim, we are in trouble!
The westerly face where we fly off the Orme is 520ft (160m) to start with!!
The guys who fly further in land will also be above this height to start with.
Comments?

Only if the model ( and yes, I know some are ) are 7kg+ which is around 15lbs in old money, and therefore a pretty big model.
The reason I reckon its seal level is because the restriction is surely to avoid potential collision with other airspace users such as real aeroplanes!

AGL get's my vote, if flying off the likes of Denbigh moors you'd be illegal at take off more or less.

Interesting....but does anyone know for sure

If it was ASL you'd have to know the HASL of any flying site you used.

Good point.
You'd think the BMFA CAA et al would make it clear in the relevant documentation.

Here you go. Taken from the BMFA handbook page 15: -

(c) at a height of more than 400 ft above the
surface unless it is flying in airspace described in
sub-paras (a) or (b) and in accordance with the
requirements for that airspace.
(i.e. in any uncontrolled airspace. A further point is
that ‘above the surface’ means ‘above the point of
launch from the ground’ and this has been clarified
with the CAA on several occasions - Ed).

This says quite clearly it is 400ft above the point of launch

Thanks Allan, I must read more carefully

Interestingly, theoretically, if say a glider was launched from the highest point on Orme's head then one walked/flew over to the normal place, could one legally go much higher than 400 ft above that place?

Good question, and although technically the answer may be yes, I reckon if one was to have an "incident" and bring down a full size or whatever, I think you'd be in deep doo doos.

Very very deep doo doos!