Two points to start with:
1) Over 85% of drugs intercepted in the Caribbean, by whatever method (Nimrod, RN, psychics, satellites, UFOs, take your pick.....) are destined for the USA, not Europe or the UK. The majority of drugs coming into UK do so from Europe, generally having originated in the Far East. If you seriously want to help stop drugs getting into this country, beef up UK customs border checks, don't buy an MPA fleet.
2) Why is it that whenever anyone talks about the free passage of maritime trade being interrupted (the normal scenarios are pirates and/or the closure of the Straits of Hormuz) people seem to think it is down to the UK to sort out the problem. THIS WOULD BE A GLOBAL PROBLEM (Straits of Hormuz) or at the very least a EUROPEAN PROBLEM (pirates) with a proportionate response from those effected. Yes, the UK would suffer given such scenarios but we wouldn't be alone by any means, and the response wouldn't be solely down to us.
Having said all that, I actually think the UK should get back into the MPA/MMA game - as to whether we will?
TOFO has said, quite rightly, that there is little (nothing?) new on this thread. I could summarize most (all?) pprune MPA (MMA?) threads as including, in no particular order:
Ex MPA guys saying that non MPA guys don't understand the complexities of the task, and that it couldn't be done by UAVs.
UAV guys saying ex MPA guys don't understand current, and near current, UAV capabilities, and that they're too blinkered by the past.
Non MPA guys generally saying ex MPA guys are too blinkered by the past.
RN guys saying the RAF isn't interested, and the RN will be the ones to resurrect the role.
Most UK military personnel saying the lack of a national MPA capability is an issue.
Most sane UK contributors realizing there is no NEW money to be had in the defence budget.
Various people saying the history of the Nimrod casts a long shadow, and will be an obstacle (political, long memories, RTS and airworthiness issues, etc) to obtaining a new platform.
What have I missed?