Quite often, listening to a 20th Century English composer on Radio 3, I've foolishly wondered, "is that the fella who Powell based Hugh Moreland on?". I say "foolishly" because it would take no great effort to research him. I've put an end to that foolishness now.
It was Constant Lambert. There's more detail here. And The Grauniad wrote a piece, (omitting Powell, you'll notice), on the 50th anniversary of Lambert's death. Reading about him, he sounds a lot like Hugh Moreland - I bet he'd be a great laugh in the pub.
There are lots of bits from his Romeo and Juliet at eMusic, here.
And if you like the sound of that, you can get it here.
Rio Grande was the piece for which he was best known in his lifetime, but he wasn't too happy with that (according to Ashman, writing for the Guardian) and would have preferred to be remembered for Summer's Last Will and Testament. (The text of the original play by Nashe is here, with part 2 here). You can have a listen to a scraps from both works at Amazon, here.