Mayor of London Ken Livingstone's proposed improvements to the North Circular Road were called into question this week by a report which branded an almost identical scheme as having no benefit to road users'.

The 2004 Hyder report, which was commissioned by Transport for London (TfL) and released under the Freedom of Information Act this week, concluded that the £600 million North Circular scheme, which promised major improvements for road users, provided better value for money than the Mayor's smaller Bounds Green scheme.

For more than 30 years plans have been mooted to improve junctions between Golders Green Road, Regents Park Road and the A406 with tunnels and flyovers, and to widen part of the North Circular around Bounds Green.

But in September, the plans were dropped and the Mayor decided to approve the smaller, £30m scheme around Bounds Green.

The Hyder paper concludes that the scheme shelved by the Mayor provides a return on investment and huge benefits for road users, while under the smaller scheme, traffic is likely to worsen.

TfL's Bounds Green project will produce accident and traffic benefits of only £7.9m, compared to £175m for the three major schemes, the report goes on to say. But TfL later used a different method to calculate the benefits of the smaller scheme and found that it would create £307m of benefits ten-times the amount Hyder had predicted.

Barnet Council is now questioning these figures. Councillor Matthew Offord, Barnet's cabinet member for transport, said: "We don't understand how TfL has assessed the benefits of the smaller Bounds Green scheme as being far greater than the inherited scheme. The lack of information about this makes it difficult for residents to see whether it offers value for money."

But Mr Livingstone defended his position, saying: "There was a very positive analysis for the scheme that we are doing, and not a very good one at all for the mega-flyover the larger schemes."

The TfL plans go on public exhibition from today to next Tuesday at the Trinity-at-Bowes Methodist Church, Palmerston Road, Palmers Green.