A public policy researcher said on Monday that the government's idea of taking a more tolerant approach to illegal structures at homes in urban areas risks undermining the authority of the law and could be unfair to taxpayers.

Ho Lok-sang, director of the Pan Sutong Shanghai-Hong Kong Economic Policy Research Institute at Lingnan University, made the comments on RTHK's Hong Kong Today programme in response to a suggestion from Development Secretary Bernadette Linn.

Linn suggested on Thursday that the administration was open to extending a system applied to village houses in the New Territories, under which householders declare minor illegal works. If inspections show the work to be safe, owners are allowed to keep the structures.

Ho said legalising structures that were safe was a good idea, but he told RTHK's Janice Wong that any changes to the system must avoid giving homeowners an incentive to make illegal alterations.

"Well first of all, if it's illegal it should be punished. Number two, if it is already in place and if it's safe, tolerate it but tax it, so you don't give them any unfair advantage," the scholar said.

The question of illegal structures has been in the spotlight in recent months. In February, the Ombudsman noted what it said were serious delays in taking action on unauthorised work found at village houses.

In September, government inspectors found illegal structures at around 70 of the 85 homes inspected at the luxury Redhill Peninsula development, which was checked after a landslide during a massive rainstorm earlier that month.