Try the following extract from Laws and Rules -
In IMC conditions outside controlled airspace above 3,000ft power aircraft can be expected to be flying according to the quadrantal height rule. "then goes on to describe the rule and also refers to flight above FL245"
NOTE - SINCE GLIDERS ARE ALWAYS EITHER CLIMBING OR DESCENDING AND NEVER IN STEADY LEVEL CRUISING FLIGHT, THE "QUADRANTAL RULE" IS IRRELEVANT TO THEM. THERE ARE THERFORE NO SPECIAL RULES FOR IFR FLIGHT BY GLIDERS OUTSIDE CONTROLLED AIRSPACE AT ANY HEIGHT EXCEPT FOR MINIMUM HEIGHT SPECIFIED IN RULE 29 (1000FT MIN ABOVE HIGHEST OBSTACLE WITHIN 5 NM. UNLESS NECESSARY FOR TAKING OF OR LANDING. OR ON A ROUTE NOTIFIED FOR THIS PURPOSE OR FLYING AT AN ALTITUDE NOT EXCEEDING 3,000FT AMSL AND CLEAR OF CLOUD AND IN SIGHT OF THE SURFACE. COLLISION AVOIDANCE IS BY SEE-AND-AVOID AND RANDOM SEPARATION.
Since a Glider Pilot does not require to hold a licence there is no restriction on flying under IMC outwith controlled airspace above 3,000 ft. As stated above a glider cannot comply with the quadrantal rule as it would effectively have to fly in a fixed rectangle as it either gained or lost height.
In class "G" airspace there is no requirement under IFR to have Radio or indeed be incontact with ATC. Separation is Not Provided and the Flight Information Service is only as good as the number of aircraft known to the controller or actually speaking to him/her. This is of course subject to flying at an airspeed below 250 knots.
There is an allocated gliding frequency of 130.4 for cloud flying gliders and there is also a requirement for any glider entering cloud to call on this frequency prior to entry. There are also other rules in repect of permitted methods of entry and proximities to gliding sites but these are irrelevant to this debate.