I think you Brits are stuck with the F-35 because of the new carriers. Both are designed for VTOL aircraft. There were plans to build at least the second one with a CATOBAR configuration. But this was turned down due to the high costs. So if the F-35 fails the two new carriers wouldn't have any fixed wing aircraft and require expensive changes.
(Not a weapons expert by any means. So please correct me if I'm wrong)