The viability of slate quarrying in the Lake District is 'under threat' after national park bosses bowed to demands from UNESCO to severely curb the 800-year-old industry.

The United Nations organisation asked for 'assurances' that quarrying activities would be 'progressively downsized' as a condition of granting World Heritage Status.

And this week those assurances were given by UK government.

Lakes heritage expert Alistair Cameron reacted with alarm, saying he was 'very worried' about the impact of downsizing on jobs and feared this was the beginning of the end for what has been very much part of the history and culture of the Lake District.

In its Local Plan Review, the national park authority said it accepted that slate quarrying was part of the 'cultural landscape' of the Lake District and recognised its historic significance.

However, the authority has agreed to restrict slate quarrying in the county to only provide material that 'meets a local need for building stone or roofing slate' or which 'meets a need for conserving buildings of national significance'.

This suggests that in future slate quarrying would be not be allowed for the production of decorative items, including head stones, plaques, house signs and kitchen worktops.

Also, the quarries would not be allowed to provide roofing slates for other parts of Britain, unless to conserve buildings of national significance where it has been used, such as Buckingham Palace and Scotland Yard.

Mr Cameron, an author who has written extensively about the slate and ore mining industries, said: "It was the norm in Coniston that everyone's dad or grandfather worked in the slate industry. Many of those who were born and brought up in the Lake District will feel extremely concerned at this proposed action."

"You can't deny that UNESCO don't like extraction being done on site as it affects the landscape but by applying this restriction they will wipe part of our history and our culture.

"At an estimate this will mean reducing the total level of production to approximately 10 to 15 per cent of the current level."

The distinctive green Westmorland slate was formed from fine-grained volcanic ash, and is part of the Borrowdale Volcanic Group, which erupted in the Ordovician period between 400 and 450 million years ago.

Honister, one of the mines which still extracts this particular slate, is also an important tourist attraction, providing guided tours for visitors. At this stage it is unclear whether the UNESCO restrictions would have an impact on non-quarrying side of the business.

Many small quarries around Cumbria operated as independent companies in the 19th century before being taken over by larger concerns.

The Burlington Slate Stone company, which produces slate for roofing and flooring and interior design, predicted it would be impacted by the outcome.

Quarry manager Ian Kelly said the company was in discussions with relevant authorities on how to move forward.

"We are aware of what is happening and we are still in consultation," he said. "It will have a big effect on us one way or another. We just hope we can sort it out with the authorities in a sensible manner."

Mike Croasdell, a former quarry wagon driver at Bursting Stone quarry, which was situated on the side of 'Coniston Old Man' and is now owned by Burlington stone, said the restriction would have a negative impact on local small communities.

"It's their bread and butter for many of us," he said. "I fear for the future of the industry and for the towns and villages that still heavily rely on slate quarries."

Paula Allen, strategy planner with the Lake District National Park Authority, said the proposed policy on mineral extraction was consistent with its Local Plan and the authority would continue to support the extraction of building stone and slate where this was 'principally needed to maintain the special quality of distinctive buildings and settlement character'.

She added: "It is important to note we will also support the extraction of high purity limestone where it is necessary to support manufacturing processes of local and national importance. Quarrying and mining has progressively downsized over the years to the point that there are now only nine active building stone quarries and three active and one inactive hard rock quarries providing limestone, igneous and sandstone rock.”