He says it could mark the start of a completely new attitude to development within the national park and eventually halt the drift of young families into towns.
National Park officials have said they are prepared to take a more positive approach to self-build schemes and succession homes – to allow sons and daughters to build their own properties when they take over family farms.
And there will also be appropriate encouragement for new business start-ups.
The shift in planning policy follows a hard-hitting report into the housing problems facing young families on Exmoor where demand for second and holiday homes has pushed house prices up way beyond anything that can be afforded on local wages.
There have been criticisms that what little sustainable housing has been provided has not been suitable for agricultural workers. And local families say their building proposals have often been summarily turned down by planning officials while incomers who have been able to afford costly legal advice have often managed to circumvent the objections.
Mr Liddell-Grainger said it was not surprising Exmoor’s young people felt they were getting a raw deal.
“Many of them feel an understandably deep affection for the area where they were brought up and want their own children to have the same experience,” he said.
“But - and perhaps as never before – planning policies and property prices have combined to prevented scores of young people living that dream.
“If we don’t make it possible for the next generation of farmers to step up, if we don’t allow people to build suitable affordable homes, if we don’t encourage the creation of new business opportunities the Exmoor community is simply going to disintegrate.
“Exmoor must remain – as it always has until the last two or three decades – a place for people to live and work and the responsibility rests on the shoulders of the planning department to ensure that happens.
“Otherwise Exmoor will die. It won’t just be preserved in aspic – as some people claim the current planning policies are designed to achieve. It will be dead: pickled in formaldehyde, its economy wrecked for ever.”