In IMC, in controlled airspace where radar is not used, what does GCAA Part 19 require after an aircraft fails to report over a compulsory reporting point because of a communication failure?

1. Maintain the last assigned speed and level, or the minimum flight altitude if higher, for 20 minutes, then adjust according to the filed flight plan
2. Immediately climb to the maximum operating altitude of the aircraft
3. Divert to the nearest uncontrolled airport and land immediately
4. Return to the departure airport via the shortest routing possible