Interesting dilemma and almost certainly a PR12 option being looked at. the bottom line is that the MoD has Billions of pounds to save and is anticipating an increase in Defence spending in about 2015 (which probably will not happen). It has to save the money somehow and reversion to B will be one of the options presented.
The option that should be presented IMHO, is to bin F35 altogether. It is unaffordabble and this obsession with getting a 5th Gen platform is putting the rest of Defence at risk. Convert the Carriers to cats and Traps and buy F18s or Rafale. This in itself will save billions and pull the MoD out of some of its current mire. The problem is that the 2 winged master race are fixated on F35 which will probably be their last manned aircraft before wholesale move to UAS/UAV/RPAS. It is about bums on seats for the future leaders of the RAF (who cannot be anything other than fast jet pilots!)
An F18/Rafale buy will plug the capability gap until future UAS become more affordable/capable. An F18/rafale buy will enable money to be flexed into other areas of need including ISTAR, AT, rotary lift etc. An F18/Rafale buy will however, pull the rug out from under the RAF as it will be a force predominantly occupied with naval aviators.
It is simple ecomnomics. 'Love, we cannot afford a Jag or an Aston Martin, lovely as they are but we can afford a whole fleet of reasonably priced cars and when one is broken we just use another!'