There are about 31 million sheep in the United Kingdom, just over one sheep for every two people.

More than half of them are killed annually for their meat. Last year the total was about 17 million.

That still leaves a lot of sheep, and farmers say they now cannot sell the old, worn-out animals. Some have been dumping them at animal rescue centres.

Questions to answer

So the National Farmers' Union, which represents farmers in England and Wales, has welcomed Agriculture Minister Nick Brown's announcement that he is considering a mass slaughter of unsaleable sheep to help raise prices.

But some hard questions need answers before any such scheme can start.

Lambs will sell, but not their mothers

The first is whether Brussels would allow it. The European Commission ruled not long ago against the introduction of a similar (though not identical) cull in Ireland.

The UK's proposed ewe cull (it would apply only to older ewes, not to lambs) would not pay farmers anything.

It would slaughter their animals free of charge, relieve them of the expense of feeding and caring for them, and - so they hope - breathe new life into the market.

Even so, Brussels might still judge the scheme to be a subsidy and it is not certain it would agree.

If it did, the next question is how much the cull would cost. Brussels would probably agree to pay something, but British taxpayers would pay the greater part.

The total cost would depend on the number of animals involved and the Ministry of Agriculture wants the NFU to suggest how to decide this.

Meat destroyed

The number of cull ewes could be a million animals, or possibly more. They would all be past breeding age, so at the end of their economically useful lives.

But farmers may be pressed to set an age limit to reduce the total they want killed to manageable levels.

No meat from the animals slaughtered in the cull would be sold. Their carcases would be rendered and sent for incineration.

Few farmers will want old ewes in winter

There is already a huge and growing backlog in incinerating the remains of cattle slaughtered in the BSE crisis. Adding sheep to the pile would increase the costs.

The main cattle cull is the Over Thirty Month Scheme (OTMS), designed to take cattle above that age out of the food chain as younger animals are believed not to harbour the BSE agent.

In an average week, 15,000 cattle are slaughtered under the OTMS. Last month the House of Commons public accounts committee said the ministry had been "weak" in its introduction of the OTMS in 1996.

Industry sources say the ministry and the Intervention Board, which buys in farm surpluses to protect prices, have learnt their lessons from those days.

They have now built up contacts with the abattoirs and rendering plants which they think will make them more efficient and could quickly introduce computerised record-keeping for a ewe cull if it went ahead.

The minister is also asking Brussels to introduce a Private Storage Scheme for UK sheep meat, to pay abattoirs to freeze and store meat for up to seven months in the hope that prices would stabilise.

Last year the board successfully tendered to run two similar schemes.