Wharburtons Gluten Free Tiger Bread
Wharburtons Super Soft Gluten Free buns (they are square)
Schar Panninis
Marks and Spencers GF bread is good but we don't get it often as there isn't one near us.
you can also get quite good gluten free bread from Wheat Free Baker, our favourite is the white loaf www.wheat-freebakerydirect.co.uk/product-page/white-loaf
I know you only asked about bread but other useful things to know if you if you are new to gluten free:
For pies try Jackson's bakery www.jacksonsglutenfree.com/
Morrisons do great margarita / pepperoni pizzas in the gluten free freezer or even better if they have a fresh pizza counter they can do you a normal 'pick your own' toppings pizza on a gluten free base. You do have to watch the people on the fresh counter though to make sure they use fresh spoons/ sauces etc though.
Sainsburys, marks and spencers and aldi all do battered fish/tempura chicken type stuff thats gluten free
you don't need to buy special sauces etc from the gluten free isle in most cases. Most of the usual dolmio type pasta sauces in jars are gluten free anyway EVEN the white sauce for lasagne etc.
The main things that catch people out are things like chips, crisps, sweets and chocolate, lots of cheap cola and fruit juices where you might not expect gluten to be used but often is.
McDonalds - the fries are gluten free and if you take your own bun and order a burger without the bun and are willing to out it together yourself from the bits they put in the box then the burgers are gluten free too.