Hey EnglishAL, I'm not sure if your comment "The the microlight lobby can go on flying without one, gliders can as long as they stay below 3000' " is well intended, or said tongue in cheek or intended to be inflammatory but it suggests a complete misunderstanding of the modus operandi of gliders in the UK.
For cross-country flight in a glider I prefer to be between 4000'-6000' as this gives me sufficient gliding range to search out thermals and stay within reach of friendly airfields and glidng sites. At 3000', assuming flying in still air (a fairly rare situation), a glider is typically losing 150'-180' per minute. So a maximum height of 3000' gives a useable period for soaring/searching for thermals of around 12-15 minutes (allowing for a safe circuit). At 60kts that equates to a range, at best, of 15nm. Would you be comfortable on a three hour flight having to choose a field to potentially land in every 15 minutes ?
If you genuinely don't know much about glidng then I'd suggest that you go and visit a gliding club that does cross-country soaring and chat to the members about the typical height operating bands....see if you can have a flight too but beware, you might enjoy it!