Graft-busters launched an investigation yesterday after lawmaker "Long Hair" Leung Kwok-hung claimed a mystery man offered to pay him to support the government's electoral reform plan, likely to be voted on this week. Without naming anyone, the Independent Commission Against Corruption said last night that the bribery claim made by a legislator was "serious in nature". "In the light of the significant public concern caused, the ICAC considers it to be in the public interest to confirm an investigation into the allegation is being undertaken," the anti-graft agency said. A day earlier, Chief Executive Leung Chun-ying had questioned if the League of Social Democrats chairman had not only made up the HK$100 million offer to buy his vote on the Legislative Council, but fabricated the whole story as well. He urged the pan-democrat to come clean and report to the ICAC as soon as possible. READ MORE: CY Leung tells 'Long Hair' to come clean on HK$100m bribe allegations Lawmaker Leung first went public about the alleged bribe on Saturday, claiming someone called him for a meeting in February and offered him HK$100 million to vote yes on the reform. But that night, he admitted to the South China Morning Post he had made up the astronomical figure to ensure the media reported it, though he stood by his claim of having been approached with money to change his vote. Earlier yesterday, the lawmaker told Commercial Radio he had not divulged his February meeting with the "middleman" - except to people close to him - thinking it was not important. He was clueless about the middleman's identity anyway, he said. Leung said he finally went public because he wanted to stop speculation that people were approaching him in efforts to buy pan-democratic votes. Democratic Party chief executive Lam Cheuk-ting, who is a former ICAC investigator, urged Leung to provide more details to the agency instead of thinking it was futile to report the case. "If his claim is true, it obviously involves a bribery attempt and the sum [involved] is huge. That is serious," Lam said. "He should not try to do the ICAC's job. Maybe there are CCTVs in the area [where they met]. Maybe the ICAC can trace the caller. Leung should do what a responsible resident does when witnessing a crime."