In wave, in blue hole at cloud level, hole closes, in IMC, then what?

You have already had a couple of sensible replies. It is early days in terms of formalised regulation and training for cloud flying in the UK. My club plans to offer suitable training in a motor glider but has not yet started to do so. In a year or two there may be better defined training programmes..

Up to now, pilots who cloud fly have generally been self taught, learning by trial and error. I wonder what you understand by 'basic IFR training?' I have an IMC rating for my single engine PPL - a low level rating for flying in IMC, which you can get after 15 hours flight training and practical and written tests. The tests include partial panel recovery from unusual attitudes. This was sufficient to get me grandfather rights for the future EASA cloud flying requirements. It was also sufficient to make me comfortably able to thermal in cloud with the benefit of a an A-H. However, when I do so I know that I am vulnerable to not having the resilience or redundancy of instrumentation required for powered flight in IMC. My backup plan for loss of control or instrumentation is to open the air brakes before the speed gets high.