I've recently noticed that Warburton's now has gluten-free breads and rolls, at least at a local Waitrose. I've not yet tried it, though. If you have, please submit a comment.
It seems to be about 50p more for a loaf than Genius bread. Also note that Genius breads are (still?) based in Edinburgh.
Back in March I wrote a piece looking at whether it is worth making your own bread.