Many thanks factor-fiction for your response. I sincerely apologise for my 'faux pas' is keying in incorrect letters as part of the solution - these should have been ??R?E?A - ???E???L (The clue was in BBC Music Magazine)
Hi- I think this has now been answered correctly by Fibonacci as Perfect Interval. I was only suggesting you try Crosswords rather than Q&P because I have never seen an unresolved question in Crosswords whereas some in Q&P can get overlooked like yours nearly did