Taxi union leaders and 20 drivers staged a slow drive from Wan Chai to government headquarters in Central yesterday to demand longer tax breaks for the switch to less-polluting fuels. The group plans to meet Secretary for Environment and Food Lily Yam Kwan Pui-ying this week to push for extending the tax break on ultra-low sulphur diesel to the end of next year. They are also seeking a two-year extension on the application deadline for a government grant to help convert to liquefied petroleum gas (LPG) taxis. The Taxi Operators Association, representing about half of the 15,000 urban taxis, said the period of concessionary duty was not long enough to encourage drivers to switch to the new fuel. Association chairman David Leung Shiu-cheong said: 'With a quarter of the taxis [in] negative equity, the Government should assist further by extending the new concessionary duty to the end of next year. 'Some may say we have no right to ask for more as the Government must not be held responsible for individuals' mis-investment, but our case is different because our fare and operational structure are bound by the authorities.' The Legislative Council last Tuesday approved a proposal to introduce a concessionary duty of $1.11 per litre between July 7 and December 31, this year. Duty will increase to $2 thereafter and for regular motor diesel will be restored to $2.89 per litre. The Government estimated that if all diesel vehicles switched to 'green diesel', respirable particulate and nitrogen oxide emissions - key elements of air pollution - would be reduced by 15 per cent and five per cent, respectively. At present, a one-off $40,000 grant to switch to LPG will be offered to owners of all diesel taxis up to 2001, when the scheme will be restricted to those cars less than seven years old.