Further to my earlier posts: once I started taking a higher daily dose of PPI (Lansoprazole) I felt worse. Stopped and after 36 hours felt good again. Tried Zantac: same result; stopped and after 36 hours felt good again.
Checked with doc and he said he had heard of cases of people suddenly not tolerating certain PPIs, particulalry if they had heliobacter in the past (I have).
I'm now on industrial strength Gaviscon (prescribed in 500ml bottles) and the symptoms are controlled well with this. Still got the acid and (now reduced) gurgle and still have to have endoscopy as a precaution; but strange that what should make you better can make you worse!