The Liberal Democrats have written to the government to demand action after it emerged that a flagship college intended to train engineers for the HS2 project had taken legal action to cover up a damning Ofsted report into its failing.

The letter from the interim leader, Ed Davey, along with Layla Moran and Munira Wilson, who speak for the party on education and transport, blamed “dither and delay” on HS2 for some of the problems experienced by the National College for Advanced Transport and Infrastructure (NCATI), which has attracted only a fraction of its planned student intake and required a £4.5m public bailout to sign off its accounts.

After long delays and speculation the government may scrap the high-speed rail link from London to Birmingham and then on to Leeds and Manchester, Boris Johnson finally gave the project the go-ahead this month.

The college, which has campuses in Birmingham and Doncaster, was originally called the National College for High Speed Rail but changed its name last year after struggling to attract students amid doubts the HS2 project would go ahead.

Launched in 2017 with the aim of taking on 1,200 students and apprentices a year by 2022, the college reportedly signed up 96 for 2018, rising to 335 last year.

This month, it instructed lawyers to seek judicial review to prevent the release of an Ofsted report giving it the lowest inspection grade of four. The case has since reportedly been dropped.

The college has also refused to publish board minutes, arguing they could prejudice a now-published report into HS2. Last year it was threatened with being struck off the register of companies over late accounts.

Writing to the education secretary, Gavin Williamson, and the transport secretary, Grant Shapps, Davey said: “To date, the Conservatives’ record on HS2 has been characterised by dither and delay. The government’s utter failure to manage HS2 properly – particularly its costs – is now having a knock-on effect on training the technicians we will need to deliver HS2 on time.”

In particular, Davey argued, NCATI “has been thrown under the bus by the government’s indecisiveness on HS2”.

“Next week, Ofsted will report that the college has been graded inadequate,” he said. “The college has failed to meet its learner targets, because HS2 has not appointed contractors on time, meaning there isn’t enough demand for new rail apprentices.

“Rather than being transparent about these failings, the college suspended publishing its board minutes – claiming they would prejudice the government’s review into HS2 – and attempted to gag Ofsted from publishing its inspection report.

“Is it right that a college that received a £5m bailout from the taxpayer to stay afloat should be using this money to suppress a report into its failings?”

The college, Davey wrote, affected not just training for engineers for HS2, “but the workforce that will be vital if the government is to meet its pledges to reopen much of the Beeching closures”.