.. For the UK, the F-18 is just as solid of a viable alternative for
the JSF as it is for the Marines.

I suspect that the UK wants the STOVL version to allow it to be deployed (in
emergency) of other RN flat tops and large aircapable ships (e.g. Bulwark,
Albion, Ocean etc.) rather than just the two CVF. The lesson from the
Falklands was that you had to have two operational decks to carry out real
war operations if there are no land fields available to you. If one CVF was
in refit, therefore, one could no launch any independant actions.

David