South West landowners hailed moves to allow developers to convert disused barns and other agricultural buildings without planning permission as a "victory" in the fight against time-consuming and costly bureaucracy.
Environmentalists warned of increased development and traffic in picturesque areas, and feared a rash of "unsightly" buildings that could be later converted into more profitable housing.
Planning Minister Nick Boles also unveiled plans to slash red tape on transforming disused offices into housing, designed to cut the costs of creating affordable homes and regenerate run down areas. Ministers believe up to 5% of vacant offices could be converted into flats, creating almost 130,000 homes.
John Mortimer, South West director of the Country Land and Business Association, said: "This is a great victory. It means farmers and landowners can use their redundant agricultural buildings for new growth-boosting ventures such as shops, restaurants, small hotels, leisure facilities and offices, without having to go through the whole planning application process which can be both difficult and costly."
New permitted development rights, allowing redundant offices to be converted to houses, will remain in force for the next three years, which could be applied in rural areas, Mr Mortimer added.
He said: "This will give more flexibility for owners of redundant office buildings to provide much-needed homes in rural areas and the whole raft of changes will help to underpin farming businesses and boost the rural economy in the South West."
But the Campaign to Protect Rural England (CPRE) raised concerns over damaging the character and beauty of the countryside.
CPRE is urging the Government to provide more detail about the conversion of farm buildings, warning that without clear conditions on when the new rights could be used there is the danger of unleashing on the countryside a wave of "unsightly 'barns'" that are intended to become houses at a later date.
Paul Miner, senior planning campaigner for the CPRE, said: "We are concerned that old farm buildings could be converted in completely inappropriate locations such as on narrow country lanes with poor access, and that the changes could be exploited by unscrupulous landowners to erect so-called 'farm buildings' which then become an office, and then a house without any planning oversight."
It argues landowners have used legal freedoms, dating back to the Second World War when Britain sought to be self-sufficient in food, to build large "agricultural barns" without full planning permission.
In some cases, it goes on, the "barns" have gradually grown or taken on the appearance of houses, which would need full planning permission.
Communities Secretary Eric Pickles said: "We want to promote the use of brownfield land to assist regeneration, and get empty and under-used buildings back into productive use.
"Using previously developed land and buildings will help us promote economic growth, provide more homes and still ensure that we safeguard environmentally protected land."
