Cambridgeshire guided busway consultancy fee triples
The company brought in to oversee the contractor's work on Cambridgeshire's guided busway has charged the county council almost £10m for its services.
Engineering company Atkins was expected to charge the council £2.9m.
However, contractor BAM Nuttall handed over the busway more than two years later than planned and Atkins' charges have continued to mount up.
The council says the costs will be "offset" against fines imposed on BAM Nuttall for late delivery.
The company has been fined £10.8m for failing to complete the busway in time for its planned opening in spring 2009, and failing to meet further deadlines.
Bob Menzies, head of busway delivery at the council, said: "BAM Nuttall finally delivered the scheme two years late and now dispute they should be liable for the overspend as set out in the contract.
"The council has no choice but to bring in extra resources to manage the contract and make sure that BAM Nuttall's claims are properly assessed.
"To make sure best value is delivered for Cambridgeshire taxpayers in the long run, the council must take the correct advice, which comes at a cost."
A spokesperson for BAM Nuttall said it was "unable to make a comment due to contractual reasons".
Atkins did not wish to make a comment.