Two of the four pioneering privately financed roadbuilding projects
failed to save money for the taxpayer, according to a National Audit Office report.
The schemes were expected to produce savings of pounds 168m compared with conventional roadbuilding processes. But the four contracts are likely to generate savings of only pounds 100m, the audit office report concluded.
And two of the projects - the A419/A417 between Swindon and Gloucester and the A69 between Carlisle and Newcastle - have proved more expensive than a non-private scheme would have done.
The report said the over-estimation of savings was due in part to the Department of Transport using a Treasury-recommended 8 per cent discount rate rather than a 6 per cent rate recommended for privately financed projects.
The NAO also said savings to the taxpayer may also have been affected by the Department of Transport's decision to use "shadow tolls" - where roadbuilders are paid for generating traffic - as the primary means of payment to the road operators.