OK I'll mark this one solved even though I'm not entirely certain it is - or what actually cured it!
From 28/10/15 to 21/1/16 ( roughly 3 months) I had 48 BSOD's. As I don't use the PC every day there were many nights when I had 2 or 3 crashes. After installing the additional memory (see post #29 above) I went 18 days without a problem. Then it crashed once followed by another 2 days later. But since I've had 6 days of fairly heavy use (for me - everything is relative) without a problem. So I think I'm ahead at the moment....

Ian C