There is no certainty that the London Underground public-private partnerships will provide value for money, parliament's spending watchdog has reported.

According to the National Audit Office, there is "limited assurance" that the price of the three Tube PPPs is reasonable, and "some uncertainty about the eventual price although any price revisions have to meet tests of economy and efficiency".

The contracts cover £15.7 billion of investment over the next 30 years. Shareholders in the consortiums involved in the deals stand to receive nominal returns of up to 20 per cent a year, about a third higher than on other recent PFI deals.