Because no progress payments are made by the public sector under a PPP, the contractor or consortium bears a financing cost during the construction period and therefore has an incentive to optimise the speed of construction. This could be a useful source of cost savings.
This benefit could also be obtained by way of a 'fixed price / no progress payment' contract (which is a variant of D&C).
The more general issue of the cost of private finance compared with government finance is discussed in chapter 7 (see 'Finance'). It concludes that we have to assume that the cost is the same.