Earlier posters who claim have run MOD programmes to time and cost will almost certainly confirm they they didn't keep changing the requirement or interpretation, every week
That goes without saying! Which is what I meant by management of DEC. (And I didn't claim, I stated fact!)
But there are also occasions, especially in complex programmes, when the spec MUST evolve (as opposed to the requirement changing), as designs in parallel programmes, which must later be integrated, evolve. You must be able to foresee this and make allowances up front. Such foresight requires experience and knowledge.....and full circle back to MoD's most basic problem. For 20 years and more it has not been policy to employ experienced or knowledgeable people as PMs. MoD's corporate knowledge has long gone.
The answer lies with both DE&S and DEC. If DEC tries to foist changes on the PM, he must declare planning blight if it affects his time, cost or performance criteria. OK, so he's unpopular. But only once, with that DEC, because it places the onus squarely at DEC's door to get it right first time.
I appreciate events can occur which are outwith DEC's control. But, similarly, it is up to them to take the lead and declare blight, not hide away and hang the PM out to dry as so many do.
This is where GOCO (or whatever it's called today) is beneficial. A formal contract exists between the contractor and MoD, and is (obviously) enforceable in a way Service Level Agreements are not. If MoD go into this blind they're in for a shock when the contractor tables his terms and conditions. Chief among them, penalty payments for changes.