Costs for the Fastway bus service have spiralled

The Fastway bus project links Crawley in West Sussex with Horley in Surrey, via Gatwick Airport.

West Sussex County Council has been informed that its share of the cost would increase by �6.2m to nearly �30m.

Council leader Henry Smith described it as "totally unacceptable" and said independent auditors would be brought in from another council.

Fastway allows specially-designed vehicles to use bus lanes and "guideways" to avoid other traffic on the route.

The scale of these cost increases [is] a source of major concern. Lieutenant Colonel Tex Pemberton, West Sussex County Council

The first buses ran in September 2003 and work on the final phase of the scheme was due to run from 25 July to January next year.

The estimated increase in projected costs has been severely criticised by the county council.

Lieutenant Colonel Tex Pemberton, cabinet member for highways and transport, said: "The scale of these cost increases and the fact they are only now coming to light is a source of major concern."

The council said it would consider whether to recover some of the �6.2m through "contractual redress".

However, a spokesman told the BBC News website that no blame would be attached to any of the contractors involved in the project until after the inquiry.

He added the investigation would "cover all aspects of the overspending".

The Fastway scheme will continue as planned and there will be no cost to the taxpayer because the council said it could move money around within its capital programme.