flexi pipe bore

I recently had a new basin unit with mixer tap fitted to my bathroom. Two weeks later the flexi pipe snapped just below thread to tap. Major disaster followed and upon investigation by reputable plumber informed me the bore wall was too thin, also the opinion from a council building surveyor. Could you tell me what is the correct wall thickness of these pipes, (this was the hot tap) as it does look rather thin for a lot of pressure to hold (looks roughly .5 mm without putting a vernier on it)?
Thanks

 

id assume it was WRAS approved, but i have just measured the wall thickness with a vernier gauge and it was .4 mm thick. There is no sign of any kink in the pipe. They come from Tecaz, supplied with the basin and tap.