I think it is worth a bit of explanation to reduce some posters fears and in anwer to the question raised by Pace.
If one were to consider there to be 2 main types of cloud. cumulus and stratus
Gliders rarely fly in stratus except when climbing into or descending from a wave climb or after a high climb on the edge of " spread out"
With cumulus, gliders only take a cloud climb when they really need to as it is not a fast way to go cross country, it is much quicker to run cloud streets and remain clear of cloud. Glider pilots will take climbs in the following circumstances;
Basically Glider pilots take cloud climbs only when really needed and seldom cruise in cloud for extended periods of time, hence the quaint " British only" quadrantal rule is not relevant.
to summarise;
If an aeroplane is cruising in stratus he is unlikely to encounter any gliders unless the met office form 215 has predicted " sig mountain wave"
If there are towering cu near areas that do not have cu forming it might be best for the aeroplane to fly round that isolated cloud rather than blasting straight through it if he is concerned.
I hope this puts some minds at ease