HS2 has become “a casebook example of how not to run a major project”, according to the latest scathing report on the high-speed rail line from MPs on the public accounts committee (PAC).

The PAC lambasted the Department for Transport (DfT) and HS2 Ltd for failing to work together effectively, and told them not to waste the opportunity to get a grip on costs during the project’s latest “reset”.

The MPs said it was “unacceptable that over a decade into the programme, we still do not know what it will cost, what the final scope will be, when it will finally be completed or what benefits it will deliver”.

The HS2 network was given the go-ahead in 2012 and was originally intended to link London with Manchester and Leeds, but will now only run from the capital to Birmingham.

The PAC said the “cycle of repeated failure” between the DfT and HS2 Ltd was “starkly illustrated by their continued disagreement on how much it will cost to complete” the truncated line. The government’s last estimated, in November 2023, was between £45bn and £54bn, and HS2 Ltd estimated between £54bn and £66bn in June.

Both figures are based on 2019 prices, but subsequent rapid inflation makes the total cost approaching £80bn today, the report found.

The committee highlighted enduring concerns about the redevelopment of Euston station and the surrounding area of London. The government ended speculation over the eventual southern terminus by confirming that the service would indeed reach central London, rather than stopping at Old Oak Common in the western suburbs, but the MPs said the DfT still did not have a plan for the work at Euston.

They concluded: “The department has failed in its oversight and financial control over one of our most important public sector projects and there is now a reputational risk to the UK.”

The new chief executive of HS2 Ltd, Mark Wild, was previously engaged to finally deliver Crossrail, the project that became the Elizabeth line, to an amended schedule and budget. Wild told committee hearings that cost escalations were partly the result of contracts with major construction firms that had been badly designed and left the risk with taxpayers. He has embarked on a review and reset of the remaining programme of works for HS2.

The MPs said they had “little confidence that the steps being taken now to control costs will make a significant difference”, but they urged: “The department and HS2 Ltd must not waste this latest opportunity to reset the programme properly, learning lessons from past mistakes and maximising for the taxpayer what value they can from this huge investment.”

A previous review was carried out in 2020 because of escalating costs and delays, but the then prime minister, Boris Johnson, decided to continue with the scheme. The leg to Leeds was allowed to lapse, however, and in late 2023 Rishi Sunak axed plans for the line north of Birmingham.

A spokesperson for HS2 Ltd said Wild agreed with the committee’s conclusion that there had been “failure in the management of HS2’s cost and schedule”.

“He is taking decisive action to get the project back on track at the lowest feasible cost,” they said. “His fundamental reset is critical to ensure the successful delivery of HS2’s goals – driving economic growth and connecting our biggest cities with fast and reliable journeys.”

A spokesperson from the High Speed Rail Group, representing suppliers to the project, said the report highlighted “the damaging consequences of government interventions of the last two years … Each and every change in scope has added to the delays and costs.”

The PAC chair, Geoffrey Clifton-Brown, said: “It is time to deal with HS2 as what it is – a cautionary tale that should be studied by future governments in how not to run a major project.”

A DfT spokesperson said: “The continuously climbing costs of HS2 are completely unacceptable. That is why the government acted swiftly to get the project back under control by bringing new leadership to HS2 Ltd, directing the company to begin work on resetting culture, schedule and costs, and reinstating robust ministerial oversight.”