It is MoD policy to require any new equipment to be supportable for at least 15 years.
Take modern electronic spares for example. No (honest) supplier is going to claim they'll be available in 5 years, never mind 15. So his bid includes a proposal to a make an All Time Buy of such risky spares, and only a fool would disagree. And you are given funding in advance to commit to these buys, while the spares are available. The quantity is calculated from the formula I mentioned, which is based on the EP parameters of the day. Until only 2 years ago that would have included Nimrod, for the next 20 years or whatever. 25 years ago that included 50 Frigates/Destroyers. And 85 RN Lynx. And 108 RN Merlins (!!). Today, we have well under half of each.
Any subsequent fleet reduction or cancellation, means, by definition, there is going to be a huge surplus. But that is not deliberate waste, as long as the correct type of spare is bought. It can be an indication of good risk management, foresight and decision making, based on the mandated instructions passed down from Government.
The PAC report paints a picture of blanket incompetence, but it is not so. There is incompetence and fraud; the problem is the PAC barely scrapes the surface, and Government / MoD condone it. Both then pick an easy target which makes good media soundbites, but doesn't stand up to scrutiny.