Chairman of the Legislative Council's public works subcommittee, Lo Wai-kwok, on Friday defended a government request for more funding to expand the Legco complex.

Legco last year approved a sum of HK$1.17 billion for the project, but it's now estimated to cost HK$1.56 billion.

In a paper submitted to Legco, the government said tender prices are higher than expected because the difficulty of the project is "unique and unprecedented".

"The extremely stringent limitation on the work arrangements and the extensive amount of works allowed to be only conducted during nighttime throughout the construction period further aggravate the complexity and escalate the costs," it says.

Speaking on an RTHK programme, Lo said the higher price tag is reasonable.

"I wouldn't say it's a cost overrun as construction hasn't even started," he said.

"The construction teams can only work overnight to avoid affecting Legco's normal operations during the day. It's challenging and therefore affects the project cost."

He also said the expansion project is needed because the Legco complex is overcrowded.