'We understand the difficulties the transport industry is facing but we cannot neglect the impact on revenue,' he said. Without providing details, Mr Ying stressed that different proposals were being considered to ensure the lower duty benefited consumers rather than oil companies.

His remarks came as legislators joined forces last night to call for an extension of the concession. A motion, sponsored by Miriam Lau Kin-yee of the Liberal Party and amended by Democrat Fred Li Wah-ming, suggested the concession be extended to December 31 next year.

The concession, which was introduced in July and expires next month, was aimed at encouraging drivers to switch to greener fuel. But oil companies have been accused of reaping unreasonable profits from the fuel as they enjoy a concession of 89 cents a litre even though the fuel is 40 to 46 cents more expensive than normal diesel.

Secretary for Economic Services Sandra Lee Suk-yee appealed for price cuts this month after suggestions the cost of the fuel was too high, despite a drop in its import price.

Ms Lau, representing the transport industry, said the industry would be the loser if the concession was not extended. 'One should not believe oil companies will not raise oil prices if the concessionary duty expires. They will only transform from stealing in the dark to robbing publicly,' she said.

Mr Li said public confidence in the Government would be shaken if there was no mechanism to monitor oil companies. 'It is just a slap in the Government's face when oil companies only reduce the price by 10 cents a litre,' he said.

Chan Kam-lam, of the Democratic Alliance for the Betterment of Hong Kong, claimed that the Government was unable to stop oil companies from reaping profits.