Had a consultation with a cardiologist from the private sector today... the good news is that he doesn't believe my symptoms are heart failure!
So working diagnosis is that I've a flare up of pericarditis and need to start back on colchicine, and he will write to my GP and nhs consultant to request I have additional tests... or if I get insurance sorted out then go back to him.
So feeling more reassured, and hopeful that this will spur things on.
Thanks to all for the support in the posts and chats!