A quick web search shows (I am sure Glider pilots can back up or contradict):
130.4 MHz Cloud flying and relaying cross-country messages only.
6.12 No glider shall enter cloud within a radius of 5 nautical miles of a gliding site, except from at least 200 feet from below the lowest part of the cloud.
6.13 No glider shall enter cloud unless all its occupants are wearing parachutes and have been instructed in their use.
6.21 Instrument Flight Rules (IFR). In IMC conditions outside controlled airspace above 3,000 feet amsl, power aircraft can expect to be flying according to the quadrantal height rule. This requires that aircraft flying
on the magnetic tracks shown below shall maintain their indication shown against these tracks with the altimeter set to 1013.2 millibars:
Less than 90 degrees odd ‘000s of feet (eg FL 90)
90 but less than 180 degrees odd ‘000s + 500 feet (eg FL135)
180 but less than 270 degrees even ‘000s of feet (eg FL 80)
270 but less than 360 degrees even ‘000s + 500 feet (eg FL 125)
From 19,500 feet (FL 195) upwards, different rules apply. (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 therefore no special rules for IFR flight by gliders outside Controlled Airspace at any height except for minimum height specified in Rule 33 (an aircraft shall not fly at a height of less than 1,000 feet above the highest obstacle for 5 nautical miles, unless necessary for taking off / landing, or on a notified route for this purpose, or cleared by a competent authority, or flying at an altitude not exceeding 3,000 feet amsl and clear of cloud and in sight of the surface). Collision avoidance is solely by see-and-avoid and random separation.
In controlled airspace, glider flight in IMC is forbidden without clearance from the appropriate ATC authority, unless specific exemptions are notified.