It subsequently named Fang Sheung Construction as the culprit, saying its workers cut steel bars used in construction to fake proper installation in September 2015, when they should have been screwed by hand into couplers on the platforms. The fault was rectified in August 2016.

Fang Sheung is voluntarily registered with the Construction Industry Council as a subcontractor specialising in “reinforcement bar fixing”. It was hired by Leighton Contractors (Asia), which won the main contract for the rail link project in 2013.

The MTR Corporation is due to release findings from its own probe next Friday, after the government demanded it do so and also arrange for an independent expert to conduct load testing on the platforms.

MTR Corp had vowed to take legal action if any evidence of fraud was uncovered, as it fended off accusations last week of a cover-up.

But on a Saturday morning radio show, pro-establishment lawmakers Michael Tien Puk-sun and Tony Tse Wai-chuen, alongside Democratic Party’s Helena Wong Pik-wan, insisted an independent investigation was necessary.

The heads of Legco’s transport panel – Democratic Alliance for the Betterment and Progress of Hong Kong lawmaker Ben Chan Han-pan and Democratic Party legislator Lam Cheuk-ting – took the same stance on a separate programme.

“You can clearly see that the government’s monitoring of the MTR Corp is ‘left hand passing to the right’ – if you sign off [on a project], I’ll do so too,” Tien said, adding that the same could be true with the rail giant’s relationship with Leighton Contractors (Asia).

Wong also stressed the need for lawmakers to conduct a parallel investigation in the Legislative Council, though this move was not supported by the pro-establishment camp. Localist lawmaker Cheng Chung-tai’s motion to set up a select committee to investigate the incident was shot down in a Legco House Committee meeting on Friday.

On Saturday, Cheung also spoke up for transport chief Frank Chan Fan, whom he said “really didn’t know” about a request made by Leighton’s subcontractor’s, China Technology Corp, for a meeting with officials last year.

The Transport and Housing Bureau earlier said the faulty steel bars incident was not reported to them but confirmed on Saturday morning that China Technology Corp, tasked with concrete pouring after the installation of the bars, had on September 15 last year requested a meeting with the bureau’s Highways Department, Leighton and the MTR Corp.

However, the subcontractor gave no specific details about the meeting agenda and then mysteriously withdrew its request three days later, saying the issue had been “resolved”. The bureau asked MTR Corp about the matter, but the rail company said it needed more information before it could comment.

“As China Technology Corp did not provide relevant information at the time, the Highways Department could not follow up,” the bureau spokesman said.

In a press statement issued on Saturday night, the bureau added that as the meeting was on “technical issues”, Chan was not informed about it.

When it was contacted by the Post, a representative of China Technology Corp said its role in the project ended in February last year but it did “outstanding works and defect rectification” in September.

He said: “We were at that moment ready to be fully demobilised … when Leighton was keeping ‘arrogant mode’ [and] denying everything, we thus [proposed] a joint meeting to settle the scandal properly.”

But Leighton’s “top figures” instead called for meeting with the subcontractor’s managing director, the spokesman continued, and they“agreed [on] certain remedial procedures to settle the scandal”. “However, we are not certain if the remedial works [has been carried out] yet,” he said.

The Sha Tin-Central line has been troubled by cost overruns and delays. Services on the Tuen Ma line are due to begin in 2019, and on the cross-harbour section between Hung Hom and Admiralty in 2021.