"the details would erode its ability to obtain value for money in future contracts"
The DWP actually seeks value for money in contracts ? Really ? Who knew ?
And how does that work anyway ? Presumably the DWP are concerned that if people realise just how much they're being ass fucked on this deal, then everyone will know they're easy ? In itself this is practically an admission - as if any were needed - that the contract involved in no way represents good value for money.
Another indicator is that the primary contractor's commercial interests could be damaged by revealing the financial model. There is but a single reason for that to be true, which is that somebody could undercut them. In which case boo hoo for them, welcome to the market, but yay for us because we just got actual value for money.
It shouldn't require an FOI, the stupid buggers would get much better VFM if they stopped trying to do all this under the table.
Paris, because she does things under the table.