i think folks are getting carried away with the maritime aspect! My understanding is that 1 Sentinel has been/will be taken out of the forward fleet for trials use. One aspect of this is looking if the capability against maritime targets can be improved.
Politicians have now wrapped this up as though the aircraft is going to be a Nimrod replacement - it is not! Whether it will be used to supplement Poseidon, who knows - it is just an R&D project at the moment!!