Decoupling this from the sensitive subject of the Nimrod and its demise the fact is most countries that do long range SAR top cover which is what this problem is all about use a long range business jet to perform the task. Cheap to operate vs a larger type, fast onto station, fitted with a door to drop rescue kit, searchlight, suitable radar (maybe an optronics turret as well) and communications kit to perform the comms relay role. Good example would be the Dassault Falcon 900 MSA operated by the Japanese Coast Guard:
Putting aside all the other more military things the Nimrod did when it comes to the more narrow task of SAR top cover shouldn't the debate be had that it is a role better performed by the Coast Guard. A business jet type can be leased on a turnkey type arrangement much like what is already being done with other Coastguard types. The deal could even be tied into the one being negotiated for SAR helicopter replacement. The pilots of this Business jet will more then likely be ex RAF anyway so there will be skill pull through. In the end we get a type suited for the role and more affordable then utilising over stretched ill suited military types.