MRA4 was a procurement and management issue, there was little other reason for its demise.
As for the lack of submarines...
Russia has 43+ active submarines. China is building a homegrown SSBN. Iran can close the straights of hormuz with 1 Kilo, given the 40% of the worlds sea-going oil transits this area, i'd say thats a big deal.
Every major player in the world is investing in MPA, except the UK.
5 years time we'll either buy old crapped out P3's, a cut down P8, or perhaps a fleet of Atlantiques/Dash8's/Challengers etc etc.