As well as the natural distrust of Brit Aerospace, should they fetaure in the propsed new UAV... in which case they'll first have to find an old UAV to reuse the fuselage...that quote re the new UAV being in service 2015-20 should ring alarm bells. At the very least, even if the new UAV could conduct ASW from the word go, that's several years of capability gap that I still don't believe we can afford.
Other UAV based solutions fall at the same fence in my view - their in service date would be similarly far off, and the cost would be high. Not as high as the cost of developing Nimrod from scratch, but then it's already paid for and whilst I'll admit I'm no expert on the cost side of thing I doubt you'll get a fleet of UAV ASW platforms for anything you could consider non eye watering.... You need:
UAVs with a sizeable sonobuoy load, there is no point in a loing loiter time if you have no stores to drop, subs tend to move out of buoy patterns fairly quickly.
The ability to take the data uplink, fire it reliably to a geostationary satellite, which can retransmit to land where suitably analysis equipment and operators are colocated with tactical staff, ie replicating the Nimrod tac area. This replication makes sense because Nim crews proved repeatedly they were extremely good at this difficult role, only an idiot plays with a effective system. The bandwidth would be quite large, you want to be able to monitor several dozen buoys simultaneously.
These two requirements suggest to me multiple UAVs per target, you'd have to look at the buoy load and dispensing capabilities to decide how many buoys you could fly per UAV, buoy setting would need to be dealt with but if you can get the rest to work then I doubt that'd be a problem.
You would probably also want a radar, you'd feel really stupid if the acoustics guys suggested the target had surfaced to fire or something and you had no way to check that.
You'd probably also want a torpedo capability, as that's the final leg of the game and there's no point having a peacetime only system.
Buoy loads, torpedo load etc - I'd be guessing, but my guess would be that you'd need several UAV's per contact, allowing for turnround etc I think the fleet would have to be a couple of dozen to replace the MRA4 on ASW.
Now we need to design and develop it, get the sensors to work on it as advertised etc.... that sounds like a long job to me. On the other hand MRA4 would (allegedly) be flying by Feb 2011, and buying a different MPA if you are allergic to Nimrod would, I think, give us our capability back rather faster than developing an ASW UAV would.
My main gripe about UAVs is that people are describing as yet imaginary systems as if they exist and are proven.... and I have yet to read any of the linked 'adverts' about UAVs that describe HAVING a capability - they all say 'are hoping to develop' or 'intend to develop' etc.
Dave