Coff, it's always down to money, as you know. The "top brass" seem to know better - every time. I fail to see how buying US F35's at some £35 million apiece (who knows the true cost of each A/C?) rather than many more F15/F18's for a fraction of the price can be a "No Brainer".
With today's technology, the A/C is purely a "launch" platform for highly sophisticated missiles/cruise missiles & air launched bombs/Nukes. Modern A/C only need high speed/endurance/long range weapon delivery & some stealth to succeed.
I would rather have 10 sqns of F18's than 1 sqn of F35's. The US can't manufacture these F35's in months should a really big shooting war start! For one F35 you could probably buy 20 serviceable F16's from Belgium or Holland...
Cameron & MOD have lost the plot. Don't even get me onto retention of expensively trained aircrew. I'm glad I got out when I did.
Anyway, there is & IMHO will never be another credible SAM defence of UK airfields/cities. There is no system commercially available at present other than Patriot, which really is short range. Israel could provide a solution but no UK Party would agree to upset the USA by purchasing from them.