1.120 Under the PFI Option, the required scope change is assumed to be undertaken by the Procuring Authority's existing PFI partner. It will therefore give rise to an increase in the Unitary Charge. The Spreadsheet accommodates this by introducing the Value that, under the PFI Option, the same scope change as modelled under the Conventional Procurement Option attracts a cost premium flexibility factor of 10% of the costs incurred under the Conventional Procurement Option. This Value, which should be tested and tailored to the particular project being assessed by the Procuring Authority, reflects the presumption that PFI is structurally less well-suited to accommodate scope changes because, for example, interface risks arise for which the private sector partner charges a premium or because of the weakened bargaining position of the Procuring Authority. It should also be borne in mind that frequent and significant scope changes introduced in the Spreadsheet will combine to erode the VfM of the PFI Option and will eventually bring into question the viability of a PFI-based solution altogether.