Value for Money
Pr00ne raises a very good point. We have the 5th largest defence budget in the world but that doesn't reflect in the size and capability of our armed forces in the global context. Obviously there is a lot of nuance in that - some bigger militaries do lots of off the shelf acquisition, use old/second hand kit or simply offset capability with numbers etc
To my mind, there are 2 reasons for the mis-match- an overwhelming and inefficient desire to achieve absolute value for money on every defence pound and strategic industrial requirements.
On the first point, whilst we absolutely do need to deliver value for money on the budget we have, there is a point in pursuit of that where that desire itself costs money. I think of the MoD scrutiny process, contracting arrangements, approvals staffing etc etc. Whenever we think we have hacked that area, another group of people, with a vote, seem to pop up and so the wheel turns.
As for industrial requirements, it is now pretty clear that the MoD is unable to run effective, competitive tenders due to national strategic requirements to maintain certain industrial capabilities. that, therefore, comes at a cost and one the MoD seems to bear unilaterally. When I last served in the MOD, there was some talk on gaining cross-Whitehall consensus on other depts. contributing to this fixed overhead, but it seems that plan went nowhere as far as I know.
At the end of the day though, we are a democracy and no matter how much we decry the spend on perceived inefficiencies elsewhere or a welfare system that seems to discourage employment and contribution etc, the (lack of) defence awareness within our nation, coupled with the Iraq/Afgh effect, simply doesn't permit the case to be made on behalf of the MOD budget.