I'll second Jayand's response.
Given that all those likely to hold power after the next general election will look to protect health and education, all other government departments will take a disproportionately large hit; including defence. So, in order to get the force structure described above the services as a whole would have to absorb further eye-watering cuts (what would you get rid of considering what little we have left?), plus cutting something else in order to get the money and personnel for an MPA capability.
We are only a third into UK austerity, with genuinely eye-watering decisions on capability to be made in the next parliament. I really cannot see anything remotely like that described above happening - as much as the argument for regaining an MPA capability is watertight based upon real world events.
Bottom line is that, sadly, it is not going to happen.
I would love to be proved wrong though.