Shell, the biggest oil company in Hong Kong, said last night it would not convert filling stations to offer cleaner liquefied petroleum gas (LPG) unless the Government put forward a better offer. In a response to government criticisms, company director Robert Young said officials had only offered to waive land premiums for their stations for an unspecified period once their current leases expired. But he said none of the leases on about 15 sites the Government targeted for the LPG taxi scheme was due to expire in the next 10 years.