Just to spell it out, the BCA insurance can be applied to foreign visitors provided they apply to become a prospective member of a club and restrain themselves to 4 trips for free or pay up for 5 or more trips (FAQ 53). But, and it is a big BUT, the cover is only for public liability. So it would not cover hospital costs if the visitor was injured as a consequence of their own fault. And note that payment is usually upfront of treatment for most things other than A&E. (Google "cost of hospital treatment for foreigners" for some detail.) And even if it were eventually proven that another member on the trip was responsible for the injury, it would be months if not a year or more for the claim to be settled. So a foreign visitor will need either a big wallet or travel insurance covering caving injuries. (That's excepting visitors from countries which have an agreement with the UK, like to EU.)