Since this accident, which I CANNOT believe was any fault of the ATCO in question, I've noticed many ATCOs providing a LARS to ac saying "Confirm you are aware that you are responsible for you own terrain clearance?" on initial contact. I don't know whether this is mandatory - if it isn't then I certainly don't blame any ATCO for the extra RT!
One used to hear words such as "Further descent will be at your discretion" passed by ATCOs to pilots asking for further descent below Safety Altitude; that could possibly be seen as ambiguous. A colleague once explained outrage to me that he'd been told 'further descent at your discretion' - and had nearly hit Didcot power station. I told him that was totally his fault, whereupon we found out that he had no idea of the limitations of the ATSU he was working at the time.... Perhaps his extensive time under positive radar control in the airlines had insulated him from the realities and captain's responsibilities of operating in IMC in Class G airspace.
But ALL pilots are taught from the start of flying training that they MUST NOT fly below Safety Altitude in IMC without radar cover WITHIN THE LIMITS of the ATSU (except for those with specific TFR etc release to service). At least, all RAF pilots are.....
Best wishes to the poor chap being put through all this pain.