Eddie1, Morris Blythman wrote the Coronation Coronach, not Hamish Henderson and I think the lyrics as well as the tune may have something to do with it not being aired.
Nothing Hamish wrote could ever have been banned as he steered clear of any specific nationalist or republican line. His songs were generally socialist and broadly internationalist, British.
A slight exception to this was his Men of Knoydart but, although it had an anti English slant, I don't think it was 'bannable' material.