Global hawk with a suitable ELINT fit. It's got +24 hrs endurance. Kit it out with a modular payload for the Afghan mission. Develop a maritime modular payload. Stop trying to buy one size fits all manned aircraft to last for 40 years. Buy modular to last 5 years tops mounted on a platform that could cover British interests from hugely long range.
Operate it from Kinloss, if the satellite geometry allows that (and the blinkered hierarchy of course!) with in-theatre troops/int specialists on a collaborative network.