sorry, forgot to add my "being facetious" tag to my comment
Personally, given the manipulation of Defence budgets and figures for political ends, I no longer pay attention to the amounts quoted. They have zero resemblance to the end cost anyway.
Thanks to the above posters for the updates re the 4xP8 rumours - interesting 'swerve' in the answer. Perhaps we should all refrain from asking these important questions on the grounds that it may " prejudice the formulation or development of Government policy." Maybe we are expected to just pay the bill and not worry about how it is calculated or what we get for it?