Journalist Andrew Gilligan has long argued for a slower, cheaper rail line to be built

The prospects for survival of the high-speed rail line HS2 look slimmer after the prime minister, Boris Johnson, appointed an arch-critic as transport adviser.

The journalist Andrew Gilligan, who was cycling tsar in Johnson’s London mayoralty, has long opposed what he says is a “disastrous scheme”, arguing for a slower, cheaper line to be built instead.

Gilligan’s reports, first for the Telegraph and later the Times newspapers, have included exposés of cost overruns and interviews with whistleblowers.

Beyond reporting on the high-speed rail project, unveiled almost a decade ago to link London and Birmingham and eventually Manchester and Leeds, Gilligan’s opposition was clear in early editorials before the scheme was officially approved by the coalition government.

Writing in the Telegraph in 2010, Gilligan said: “Virtually every argument you will hear for high-speed rail, today and in the months of argument to come, is either based on deeply shaky assumptions, or is just plain wrong.

“This line will not be green. It will not greatly benefit the economy. And, most remarkably of all, it will probably make your journey slower, not faster.”

In later reports, he described HS2 Ltd as a “mini-dictatorship”, and in a Twitter post, as a “disastrous scheme”.

Gilligan’s appointment comes as the HS2 project faces questions and its £55.7bn budget, last confirmed in 2015, is in doubt.

A letter from HS2’s chairman, Allan Cook, to the Department for Transport, leaked to the Financial Times, reportedly revised up cost estimates for the project to £70bn-85bn, partly blaming “poor ground conditions found during surveying work”.

Johnson promised a review of the project, and has confirmed he has asked the former HS2 chairman Douglas Oakervee to conduct “a brief six-week study of the profiling of the spend on HS2”.