The Department for Transport (DfT) has said a report from the HS2 management team suggesting that costs could rise by a further £9bn are not “accurate or reliable”.

An HS2 board paper released in June anticipated that the project was now expected to cost between £54bn and £66bn in 2019 prices – a marked increase from estimates the previous November of £49bn to £57bn.

But in a written statement to parliament, the DfT said the estimates did not take into account recent changes to the scope of the project, including efforts to bring in private financing for the final London leg that stretches to Euston.

“We do not think these figures are accurate or reliable,” the DfT said, while noting that transport secretary Heidi Alexander has asked the board of HS2 Ltd to provide new cost estimates “as soon as possible”.

“Since coming into government, we announced urgent measures to get a grip on HS2’s costs and ensure taxpayers’ money is put to good use. We will be working closely with the new CEO Mark...