Yes IE currently launches from a hyperlink which is as expected since the default browser is still set to IE. I have also checked the default protocols and nothing is currently set to Edge - so all good.
As I said in an earlier reply, I suspect that by uninstalling Maxthon Cloud Browser I may have identified and fixed the original problem because the default has not changed since that uninstall and previously it seemed to keep changing every few days.
My problem can be marked as solved - if it re-emerges I will re-post as a new thread.
Thanks to everyone that contributed.