Peter Chapman, vice-president of the National Farmer's Union of Scotland, said sheep farmers in the Shetlands were facing a bleak future.

He said: "This is the worst crisis to hit hill farmers, but what else can they do when these animals are costing them more money than they are worth?"

Around 20,000 Shetland sheep face death

"By the time the sheep are taken to market and the various fees paid farmers are out of pocket and they simply can't go on like that."

Crofters in Shetland have to transport their sheep more than 150 miles to markets in Aberdeenshire.

The farmers' union says if government money is not pumped in immediately then sheep farming could die out altogether in parts of Shetland.

'Cull is inevitable'

Andrew Harmsworth, a spokesman for Shetland Islands Council, said the cull was a "tragedy" but he said it was inevitable unless market prices improved significantly.

Mr Harmsworth said that the decision to cull sheep which couldn't be sold was up to individual farmers and the 100 or so Shetland grazing committees.

The mass slaughter will be supervised by the councilĀ“s environmental health officers and the Scottish Environment Protection Agency.

'Time for government to act'

Tavish Scott, who farms on the island of Bressay, said it was time for the government to commit itself.

He told the Shetland News: "We need to see a commitment for a sustainable, long-term future for agriculture. Otherwise there is no point in any of us being here."

Mr Scott said: 'We want a fair return at the market place and we want the ability to export into those markets, into which we previously very successfully exported."