I've said it before
and no doubt I'll say it again 1924 Washington Naval Treaty was when the British Empire started to fall apart. Allowing other navies (US) to match the RN and limiting the numbers so it was impossible to adequatley man three fleets (Home, Med and Far East.) this left inadequate cover to enforce rule and independances came thick and fast, dropping the net income, so the funds for ship building further.
After WWII - it had neither the money nor the inclination to re-arm and what was left of the empire disolved
with the empire disolving, so did the spending power of the government, and followed several strategic defence reviews '57, '66, '75,'81, '90, '94,'98 2003, '05, '10, '15 that have succesivley gutted the remaining resources. its a continuing trend.
If the '81 review had been earlier, the two landing ships Fearless and Intrepid (recently replaced by Albion and Bulwark) along with our new Aircraft Carrier (Invincible) would all have been sold off and the falklands campaign would not have been possible.
The escort frigates are getting on a bit now, the T-23s started in '89 and the T-26s have been delayed and decreased by successive reviews, now half of them replaced with th T-31. The T-23 were always ASW focused and worked alongside the T-21 GP frigates, that got retired and never replaced.
The Type-45 was a patch job done on the attempted NFR-90/Horizon-Class, and as such is not without its problems. It was aready cut from an initial 12 to 8 then 6 ships
the way things are going, by the time we get F-35 (wether they are Bs or Cs) the QE and PoW will have been sold off too.