HS2 is now poised to cost the taxpayer as much as £102bn and will not deliver its first service from Euston until at least 2040, according to the transport secretary who blasted the project as a “massively over-specced folly”.

Heidi Alexander said the cost of the ill-fated train line was now on course to nearly double from the previous official estimate, because of a litany of managerial missteps which sought to “gold-plate” the megaproject. The transport secretary confirmed the project will still go ahead as scrapping it would cost almost as much as continuing, but “without any of the benefits.”

“It was a massively over-specced folly with the prospect of the fastest trains anywhere in the world, tickling the fancy of Conservative ministers,” she told MPs.

“If we were a country the size of China, I could understand it, but we are not. Passengers just want reliable trains that turn up when they’re supposed to, more services and more seats.”

In a statement to Parliament, Alexander said HS2 was now on course to cost the public purse between £87bn and £102bn, a major uplift from £66bn estimated under the last official forecast.

Two thirds of the hike was attributed to “past misunderstanding of the work required” and a slew of iniefficiencies, the transport secretary said, while the remaining third was linked to the effect of inflation.

HS2 services won’t run until 2036

The project’s timeline was also pushed back drastically, with services from central London now not expected to run before 2040 at the earliest. Services between Old Oak Common – the west London rail hub where the first trains will run from – and Birmingham are now not expected to get under way until at least 2036.

The updated timeline means the project’s development from announcement to delivery is now on course to take more than quarter of a century, and cost nearly three times its original budget.

The update represents a new low in the long-running fiasco of HS2’s development. The project was first signed off in 2011, during George Osborne’s tenure as Chancellor. But since then it has been blighted by a barrage of delays, planning issues and cost overruns, and earned national derision for budgeting more than £125m for a so-called ‘bat tunnel’ to minimise the project’s environmental damage.

“If it seems like I’m angry, it’s because I am” Alexander said. “I am angry on behalf of taxpayers and affected communities who have been swindled by the failures of successive Conservative governments. I am angry on behalf of the 1,000s of rail and construction workers giving their all on this project who do not deserve to have their industry tarnished in this way.”

This is a breaking story and will be updated.