If the government wish us to have a particular aircraft because it is in the national interest then so be it - they are elected to make those decisions. However, they also are increasingly expecting the defence budget to be run along commercial lines and are funding it accordingly. Therefore if this procurement is being made for political reasons, rather than commercial/defence reasons then the extra cost should be funded from outside the defence budget.
It is also a little irksome to see BAE Systems receiving contracts on this basis when they have happily sold-off all their inherited family silver - HS125, Airbus, Rover etc - without any thought for national interest.
Politics was just as big a factor in the procurement of the A400M - which some people around here are very quick to defend.