Revised plans for HS2 should not be put into action until government is confident they can be delivered, says a new report from the National Audit Office (NAO).

The UK’s independent public spending watchdog say the Department for Transport (DfT) has made progress but must get the reset of HS2 “right this time following past failures”.

HS2 and DfT are resetting the HS2 programme. In May transport secretary Heidi Alexander announced the line will now cost between £87.7bn and £102.7bn with the first services running from London’s Old Oak Common to Birmingham’s Curzon Street Station likely between May 2036 and 2039.

The opening of HS2 had previously been 2033 with costs set at £35-45bn – she said HS2 had “already spent close to the original budget” with costs at the end of March at £44.2bn. The full route including both Euston to the south and Handsacre Junction, will not be completed until between 2040 and 2043.

NAO said a “considered approach” was being taken to reset HS2 but added “significant work” remains to complete the reset by 2027. It said this includes finalising the cost and schedule, completing commercial renegotiations, developing plans at Euston and ensuring the right skills are in place to deliver the programme.

In completing their reset of the programme, the NAO recommends that DfT and HS2 ensure that “they do not proceed with putting their revised plans into action until they are confident everything is in place to deliver against them”. The new report said they must ensure they fully put the programme “on a stable footing to avoid previous failures”.

NAO said the driving causes behind the majority of these cost increases are scope change, inefficient delivery and an underestimation of the time needed to complete delivery.

The NAO report recommends:

• Review the reset timetable in the autumn to assess whether it remains achievable
• Maintain a focus on cost, schedule and commercial management as they move into the next stage of the programme
• Revisit the governance as the programme moves into the next stages of work to check it remains fit for purpose

Gareth Davies, head of the NAO, said: “After facing historic difficulties, including significant cost increases and delays to delivery, HS2 Ltd and DfT are taking a considered approach so far in their latest reset to the HS2 programme.

“However, these previous issues highlight the importance of DfT and HS2 Ltd getting it right this time to ensure the future success of the programme. Establishing a fully robust estimate of cost and schedule, completing commercial negotiations and getting the right capabilities in place is necessary before they can complete the reset.”

Click here to read the full report.