ctctim, whilst I doubt CTC actually specify any particular sunglasses you can/cannot wear, you may find this link appropriate for the answer to your question:
Guidance on using sunglasses | Medical | Safety Regulation
Incidentally, I recently bought a pair of aviators for flying. Only after though did I discover this ariticle which stated the type I'd bought were not actually recommended! I hope it aids you in your choice.
dunelmitepilot