I have since had a reply from the UK Health & Safety people. They say that 10' high or 4 stack layers is normally OK but that in good conditions (presumably beer kegs on good pallets would qualify?) 6 high can be permitted.
Surprisingly an factory equipment suppliers catalogue shows the depot in question with 7 high stacking at around 20+ feet high!
I have suggested they take a look as 8 high is now normal there. In the picture they show a local delivery truck at around 12 feet high and the beer is clearly 10 over the truck roof height - the roof will be translucent fibreglass or thin aluminium sheeting!
I have asked about the bouncing capabilities of beer kegs from height as I believe they will rebound high enough to enter the cab area of a fork truck or can ricochet off the counterweight across the yard - perhaps even taking the gas tank as they go!!!
Any further comments would be most welcome.
Best wishes, Rod