The MTR Corp had earlier announced that completion of the project had been pushed back by two years to 2017 and its budget had snowballed to about HK$71.5 billion from HK$65 billion.

Without going into specific circumstances, Cheung said he had discussed his resignation with Leung.

“I told CY that he should be prepared,” Cheung said. “If the government couldn’t take [the pressure] any more, I’d better not drag the whole government down with me.”

At the time, Cheung said, the government was accused of withholding information about earlier signs of the delay and was urged to take responsibility for the scandal. A later investigation cleared the government, with no individual named or blamed.

“I told CY that there was no justice in politics, and nobody would talk about being fair,” he said. “At that time I witnessed all the fickleness of human nature in the political world.”

The second time he considered resigning was when the government faced legislative gridlock over a request for HK$19.6 billion in extra funding to cover cost overruns at the link.

Failure to gain Legco’s approval for the funding may have meant the mega project being put on hold indefinitely near its completion.

“I had been prepared to take all the responsibility had I to announce a halt to construction,” Cheung said. “I was prepared to resign.”

Legco eventually approved the funding request after 20 hours of discussion.

On excessive lead being found in drinking water in at least 11 public housing estates in 2015, Cheung described the issue as a “failure of the system”.

At least 139 residents, mostly children under six, had lead levels in their blood above the World Health Organisation standard of five micrograms per decilitre.

Up until then, Cheung said, the government and the safety control system did not recognise there was a risk of heavy metal in Hong Kong’s water system.

Fears of a second water scare as heavy metals found in tap water

They took water samples from empty flats not on Wong’s radar, Cheung said. It was from these samples, he said, that officers first found excessive lead, before the government’s high-profile announcement of its findings.

“If our colleagues did not actively conduct tests, this whole thing would have died down without anybody knowing,” he said.

“Isn’t this encouraging everybody to start providing unlicensed taxi services?” Cheung wrote.

Cheung said he once asked an Uber regional manager at an international forum in 2015 if they ever cared about government regulations. He did not reveal the manager’s response.