LEGISLATIVE Councillor and anti-nuclear campaigner the Reverend Fung Chi-wood is demanding that everyone in the area between the border, Tai Po and Sheung Shui be told to shelter if there is an accident at Daya Bay. Mr Fung says it is ''only reasonable'' that the 500,000 people in the towns nearest the plant - within about 30 kilometres - should be warned to go indoors if a radiation cloud is leaking out. He will meet the Secretary for Security, Alistair Asprey, next Thursday to put forward his demand. The Government says in its Daya Bay Contingency Plan public booklet that ''sheltering and evacuation will not be required'' for those beyond a 20 km evacuation zone, which covers sparsely-populated Ping Chau and Mirs Bay. However, Dr Ray Yeung Man-kit, of Hong Kong University, says his research shows everyone in the territory could be up to 100 times more likely to contract cancer later in life if they stay on the streets, where they could be exposed to radiation. The Government's Security Branch says its emergency plan was drawn up to International Atomic Energy Agency (IAEA) guidelines. But Mr Fung, a member of the Legislative Council's Environmental Affairs Committee, said the consultancy study done by the UK Atomic Energy Authority in 1987 on how to plan for a nuclear catastrophe was unclear on its recommendations for sheltering. The study says people can avoid up to 90 per cent of the radiation dose due to inhalation and between 50 and 90 per cent of the direct contact dose if people are protected inside a building, but it is unclear whether this depends on distance from the stricken reactor. Sheltering ''would be very simple, very rational and very effective'', he said. ''If you are trying to protect the people you will take every precaution.'' Dr Yeung said his results differed from those calculated by the IAEA because he had incorporated more possible wind changes into his calculations than the agency used in its established model. The IAEA model ''assumes that the wind will stay constant for the whole event'', he said. The situation ''is not as simple as in that little book [the Government's contingency booklet]''. It gives people the impression that if you are 20 km away you are all right, but by simply getting into the house that is going to save you a lot by avoiding the [radiation] doses.'' When asked why he had not formally approached the Government with his findings, he said: ''They have their own people. I'm pretty sure they are aware of this too.'' He said people should close all doors and windows, switch off the air-conditioning and seal all cracks with towels or tape when an alert was sounded. He shied away from suggesting that a curfew was needed, saying such ''a serious business'' would have to be decided by the Government. ''The choice is yours, but I wouldn't go out,'' he said. Ella Tam, of the Security Branch, said the Government could not listen to all scientists. ''Even experts have different views,'' she said. ''All we can do is to follow international accepted practice.'' She said the Government did not plan to publish another booklet.