Does it also include finding a replacement for the Harpoon and Exocet surface-to-surface missiles? The RN's surface shipping are currently capable of AAW, ASW and anti-piracy roles; but lack significant ASuW capabilities. The F35 might offer that capability; whatever state that is in concerning loadout options. Building ships is all well and good; but without armament for all three major threat vectors they are at risk of being toothless tigers.
The Navy is already screaming with personnel shortages to man the existing fleet let alone an expansion - the QE carrier being a somewhat mandraulic affair. Are we going to see significant expansion?
The submarine fleet obviously is significantly more capable of ASuW and probably better at it than the surface fleet; but again with the withdrawal of Harpoon, the lack a standoff option might be missing a significant capability.
Something competitive with the Russian/Indian Brahmos project is the sort of territory I'm thinking. There haven't been many modern naval engagements though the RN has more experience of it than most (Falklands). The overriding rule in naval warfare is to strike effectively first. Long range attack and early-warning capabilities are extremely important part of that equation. The QE class carrier is rather poor concerning EW... Even if the F35 is any good in a strike role (much rumour suggests it's pretty poor).