This is not hyperbole people. When I first moved to Bangkok, I had no idea what products to buy. Foreign labels, Thai writing and whole food cooking completely confused and confounded me. Enter Marks & Sparks.
The shopping centre down the road had an M&S store, so I was able to rely on their sauces, teas, sweets and snacks as being gluten free. Thank you M&S for having reliable labelling!
While not all of their products are available here in Thailand, you will note that many basics, like pesto, chocolate, crisps, nuts, and curry sauce are.
This website outlines their policy and has a PDF document that provides a substantial list of gluten free items.