Dyfed County Council's planning committee will face pressure to end nine years' conflict by asking the Government for a public inquiry into the future of the Gwenlais valley, near Llandeilo, in south-west Wales.
Here, in a woodland area of sites of special scientific interest (SSSIs) - described by biologists as an 'ecological cathedral of European importance' - local residents and the green lobby have resisted plans by Alfred McAlpine to invoke a 40-year-old interim planning development order (IDO) extending its limestone quarrying operations from the village of Pentre Gwenlais.
Temperatures have remained high despite a decision by David Hunt, Secretary of State for Wales, to call the issue in a year ago. Mr Hunt's apparent caution since then has led to accusations from Friends of the Earth Cymru that the Government is protecting an industry with which it has 'very close connections'.
Tim Shaw, the group's spokesman, said yesterday: 'It's yet another example of a government that seems to make one mess after another. They realise there are 630 other IDOs affecting tens of thousands of acres of British countryside.
'The documentation being accepted to justify such claims is completely inadequate. We've estimated that a third of the Mendip Hills in Somerset is threatened by such orders.'
McAlpine was expected to test its claim to mine 470 acres of Gwenlais at a High Court hearing earlier this month but withdrew, paying costs reported to be around pounds 200,000.
Sceptics had been hoping that the hearing would have settled once and for all the validity of McAlpine's IDO evidence, including the existence of a detailed geological map said to have been kept in a fire-proof box at the company's headquarters in Wrexham.
The firm had decided, instead, to register its claim under last year's Planning and Compensation Act, which requires owners of long-dormant IDOs to make their permissions public. Many such claims have lurked, unknown to potential property buyers, in obscure files since the 1940s.
McAlpine has attacked the green lobby, claiming that its campaign has put jobs at risk in a region of high unemployment. A year ago it offered, then withdrew, a compromise to reduce its quarrying in Gwenlais to 35 acres centred around old workings at Druids Crag.
The rest, including the highly- sensitive area of Carmel woods, would be handed over to the Countryside Council for Wales.
Life has become complicated for the company since the discovery near Druids Crag of a 525ft (160m) self-generating lake known as a turlough, the only phenomenon of its kind known to scientists in Britain. Experts say it would be destroyed even by limited quarrying in the area.
McAlpine, which seems to have had a robust approach to public relations, later banned from the site John Gunn, professor of physical geography at Manchester Polytechnic, accusing him of associating too closely with one of the leading valley campaigners. The ban remained in force despite a 'grovelling letter' to McAlpine from Professor Gunn.
Among protesters at today's demonstration will be John Moore, who bought a 34-acre farm in the valley 10 years ago and then discovered that McAlpine was claiming a right to work bulldozers within 50ft (15m) of his back door. Mr Moore claims that a senior McAlpine executive told him at the time: 'We own the rights. When we want your land we'll take it.'
Mr Moore said: 'We want a public inquiry because we believe McAlpine's evidence could be thrown out if subjected to cross examination. The evidence I have clearly indicates that all they've got is planning permission to work two existing quarries. They've got no map proving otherwise; there's nowhere for them to go other than down.
'This case will set precedents for other people in other parts of the country that have these IDOs. If we let this one slip that's the end of it for them too.'
Euan McAlpine, a senior director of the company, said: 'The quickest way forward is through written procedures provided for under the new legislation which . . . gives us a decision one way or the other. On that score we're confident of our case. Environmental matters aren't part of that stage so we don't feel a public inquiry is the best solution.'