I could be wrong (and happy to be corrected if I am) but I seem to recall that the contract states the MoD must use AirTanker, but can use other national or international assets if no AirTanker aircraft is available (hence the image with the German A400M here). Perhaps there is scope there to equip some Atlases with AAR kits to service RAF/RN receivers for when and where there are no Voyagers available (in the Falklands or Baltics, for example)?