As has been asked above; who exactly has said we are only going to get 9? Can you provide a link? I suspect (and hope) we shall buy all 12. We need em!
See
Nimrod MRA4 In Service Date? post #37. The Flight International article seems to have disappeared but did state:-
"The Royal Air Force is now expected to field nine MRA4s, with the programme's three development aircraft not under contract to be converted for operational use."