It seems to me that the real problem is not the JSF, but the carriers. Aldready expensive on paper, they will be even costlier on completion, so Britain might need to reevaluate this single choise. If you get something in the region of 30.000t (Italians too would be interested), RN could find the money to buy (say) 40 naval JSF, and RAF another 50. None would be pleased with the compromise, but RN will have a good portion of what it needs and RAF will have something to start with. This interim solution could save some 5-6bn (rough estimates - 2bn from the carriers and 4 from the fighters) and leave the doors open to new orders in the near future. As far as i know construction of the first keel has aldready begun, so there is little time left for this option, but it is still possible.
In my opinion there's nothing wrong with Super Hornet (or Rafale). They are both good in their own right, affordable and have plenty of improvement ahead. It's just that the F-35 is the only option that can cover both RN and RAF.