Taking ibuprofen for the rest of your life carries some risk, of course, and in three years you'll have spent as much on ibuprofen as you would on the plastic cap. Worth trying first, since you've only had this problem for a month, but not forever, I'd say.

I suspect the NHS is giving you a better price on those plastic things than we get here in the States, but I'm not sure about that. Another factor to consider is whether there's a Cambridge-area dentist who can not only make the cap, but make sure it's fitted properly and adjust it if need be. (I don't use one of these; a friend does, so I know a bit about them.)