May I point out that the planned UK JSF buy is in penny packets until the '20s. We literally plan to buy a handful. The inevitable slippage is moving that to the right.
The intention at the moment is to save money - as soon as possible. What on earth leads anyone to think the government would even consider buying a new type - in numbers - which would require a large up front payment?
I would suggest that the likely option, without a current threat requiring a carrier, is to retire the GR7/9 force early, try and sell off the first CVA to India or elsewhere (including the GR7/9 wing as air assets), and look at harmonising the entry into service of the second CVA to coincide with the purchase of the F35C.
Time to adapt the design for EMALS and spread the cost.