A plague of ticks, brought on by the warm weather, coupled with rising numbers of predators such as foxes and birds of prey, has devastated grouse populations. Stocks are now so low that some sporting estates have cancelled all shooting.
Studies published by the Game Conservancy Trust reveal that in England and Wales red grouse numbers have fallen by 10 per cent in the past year. Scotland, which endured a disastrous spell between 1991 and 1992, has suffered even greater losses. The number of birds in Perthshire alone has slumped by 12 per cent.
The Scottish Landowners' Federation (SLF), which represents 4,000 estate managers north of the border, predicts that this year's season will be one of the worst on record. Graeme Gordon, the federation's convenor, said: "After three difficult years, the birds are still under serious attack. These are very difficult times."
With some Scottish estates closed for the sixth successive year, landowners are now calling for radical action to boost the pounds 20m-a-year industry, which employs more than 3,000 people in the Highlands. They want the Government to relax the provisions of the Wildlife and Countryside Act to allow selective culling of birds of prey, including falcons, buzzards and hen harriers.
Lairds argue that recent research carried out by the Game Conservancy Trust indicates that raptors are killing increasing numbers of grouse. Measures designed to protect the threatened species have, they say, proved too successful.
John Drysdale, who has been forced to delay shooting on the 25,000 acres of moorland he manages near Inverness, explained: "Killing birds of prey has been illegal for many years and now these birds are out of balance with the grouse populations. On my estate I am seeing ever fewer grouse because they are being eaten by raptors.
"If things carry on like this, grouse stocks will never recover and I will be forced to lay off staff and turn to other forms of land management, like forestry, which will destroy the moorland. That would be a disaster."
In April this year Mr Drysdale, backed by the SLF, urged the Government to consider changing the law. Last month the Department of the Environment set up a working group to study the issue. The group comprises the SLF and conservation groups such as the Royal Society for the Protection of Birds and the Hawk Trust.
Although landowners are hopeful that the new body will recommend a return to licensed shooting, the RSPB says it will oppose any attempt to change the law. Officials argue that with more than 100 birds of prey killed illegally in Scotland last year alone, any relaxation of the 1981 Act could lead to a return to large-scale persecution which drove some species to the brink of extinction 20 years ago.
David Dick, investigations officer at the RSPB, said: "We are keen to examine all the issues surrounding the declining grouse stocks but we don't believe that culling is the solution. Raptors are still under grave threat. You can't take risks with birds that have been part of the natural environment for thousands of years. We cannot recommend the killing of any birds of prey."
RSPB officials argue that raptors are not to blame for the sharp decline in grouse numbers. Instead, they point to the widespread destruction of heather moorland since the war, through commercial forestry and intensive grazing, which has removed the birds' traditional breeding grounds.