Agree with Jack, but would say that Labour have simply been more stealthy than Conservatives.
A good example is PFI. While introduced by the Tories, in practice it is Labour who have largely implemented and expanded the policy, which has committed huge chunks of the Defence budget for decades to come, thus reducing the scope for flexibility.
Another example is the likes of QinetiQ. Such "extramural" costs were not borne directly by projects. Suddenly, and without compensatory provision, projects had to bear the cost, plus of course a whopping profit margin. To fund this unexpected burden, other capability had to be sliced off the other end. The creation of QQ was in effect a huge cut in the defence equipment budget. The same can be said for the privatisation of, for example, NARO. And so on.