New doubts were raised yesterday about the integrity of Leung Chun-ying's cabinet members as a minister was accused of abusing a civil service housing allowance by 'cross-leasing' properties with a colleague in the 1980s. Development minister Mak Chai-kwong admitted he had leased a flat he had bought to another civil servant for 27 months between 1986 and 1988 while claiming a government allowance for renting a flat from the same colleague in the same estate. But Mak, responding on Metro Radio to an Apple Daily report, insisted he did not breach any rules. 'Investment in private property should not be considered as affecting an officer's credibility if it was done legally and in accordance with the regulations,' Mak said, adding that what he did was common practice at the time. It has not been suggested that Mak swapped ownership of the flat with his colleague or had ever owned the flat he lived in, which would have breached the rules. The revelation was a potential new embarrassment for the new chief executive after he and several of his ministers and advisers apologised in recent days over illegal structures at their homes. Mak faced calls from lawmakers across the political spectrum to reveal full details of the case, while some pan-democratic legislators criticised him for abusing a grey area of the rules. Several government officials in recent years have been prosecuted and sentenced for abusing government housing allowances. Secretary for the Civil Service Paul Tang Kwok-wai declined to comment on Mak's case or say whether he would conduct an investigation. He only said the rules prohibited civil servants from renting flats owned by applicants for allowances or their family members - but that did not cover properties owned by the applicants' colleagues or friends. Labour Party chairman Lee Cheuk-yan said Mak had in effect used public money to pay the mortgage on his flat. 'The public has high expectations of ministers' integrity and moral standards and does not expect them to abuse grey areas of the rules,' Lee said. 'But Mak has apparently abused the allowance mechanism and it will undermine his and the new cabinet's credibility.' The Chief Executive's Office did not respond yesterday to questions whether Leung would instruct Tang to look into the case, after the Civic Party's Audrey Eu Yuet-mee and Wong Kwok-hing, of the pro-Beijing Federation of Trade Unions, called for a full investigation. Mak, who joined the government as an assistant engineer in 1977, said yesterday he decided to buy the property in the phase two of City Garden 'as an investment'. He then leased it to a colleague in 1986 for 27 months because 'civil servants have stable incomes' to pay the rent. His rent allowance ceased in 1988 after he was promoted and moved into civil servant's quarters.