It took a while, but somebody finally acted on those 38-year old gaskets. The BBC is reporting that the RAF's Nimrod MR2 fleet has been grounded for the replacement of the engine bay hot air ducts, the famous pipe involved in the loss of XV230 over Afghanistan in September, 2006. According to my own sources, the original plan was to have them all examined and either replace, overhaul, or ignore depending on the results, but BAE as the Design Authority wasn't keen on this (who would be?) and therefore the ducts were all declared time-expired.
The upshot is that in order to maintain the RAF's maritime commitments in the North Atlantic (which seems to be what "critical homeland security tasks" are in Bob Ainsworth's statement), they have to find enough airframes to maintain the sub-spotting and SAR quick reaction alerts while the fleet goes through the engineering wing at RAF Waddington. This means that the Nimrod detachment in the Middle East is being withdrawn.
Its tasks included supporting the various naval operations in the area (pirate spotting, looking for a dhow with Osama Bin Laden on the bridge, and looking after oil platforms off Iraq) but also providing special reconnaissance capabilities for the Army in Afghanistan, both with the Searchwater 2000 radar and also providing a live video feed. Readers with a long memory will recall that XV230 was the first Nimrod to get the video capability under an Urgent Operational Requirement for Helmand in early 2006.
Apparently "other UK or coalition aircraft" will fill the gap. The whole affair originates from one of the great cockups of British defence procurement - the much-delayed, if formidable, MRA4 Nimrod, which has been in the works since the 1980s under various titles. (One of which was "Nimrod 2000"...) The decision to convert existing airframes rather than build new, in order to save money, turned out to be a very bad one, especially as the original airframes were essentially built by hand, with the result that the new CAD-CAM'd wings didn't fit any of the fuselages and the job ran several hundreds of millions over budget and many years behind schedule. The first flight has now been achieved, but part of the problem is that the planned fleet has shrunk dramatically, and the existing MR2s have been flogged to death waiting for the new airframes.