National parks to be protected as planning reforms are amended

New framework is expected to include safeguards for some protected landscapes with environmental or heritage significance

Critics including the National Trust fear that new planning law would be a 'developers' charter'. Photograph National Trust

The government is set to make important concessions to opponents of its planning reforms, including specific protections for national parks and areas of outstanding natural beauty.

However, senior ministers remain adamant that the biggest shakeup of planning law for more than half a century remains what insiders called "unashamedly pro-growth" – making it almost certain they will not appease their critics in the environment movement.

The revised national planning policy framework will be published on Tuesday after months of opposition triggered by a phrase in the original document stating that "the default answer to development proposals is yes, so long as they are sustainable".

Critics, including the National Trust and the Campaign to Protect Rural England, warned the new regulations – which have reduced planning law from more than 1,000 pages to just 52 pages – would be a "developers' charter" and would lead to housebuilders and others "concreting over the countryside". There were also concerns that the changes would make it easier for the government to press ahead with controversial projects for high speed rail and airport expansion in south east England.

The revised framework is expected to include explicit protection for some protected landscapes with environmental or heritage importance, and for sports playing fields, and will include a definition of "sustainable development" – an omission highlighted by critics of the original. Councils will also be encouraged to consider development on brownfield sites first, addressing another criticism that greenfield sites could have been developed more easily under the original version.

However, the government's determination to press ahead with what the Chancellor last week called "the biggest reduction in business red tape ever undertaken" will be made clear by the symbolic move to further cut the new planning framework by another two pages, to just 50 pages.

Among the issues likely to be scrutinised by critics will be how much weight the definition of "sustainable" development gives to environmental concerns when weighed against economic questions, and how much protection is given to greenfield sites and to the wider countryside, which is currently recognised by planning guidance as having an intrinsic value.

On Monday night it was not clear if the revised document would preserve the phrase that the "default answer … is yes" to sustainable development, but a government insider said there was "a powerful presumption" in favour of sustainable development, and that "development should be approved unless the costs significantly and demonstrably outweigh the benefits". Should this form the basis of the government's definition of "sustainable development" it will almost certainly not satisfy environment campaigners.

The government initially dismissed critics of its planning reforms, with planning minister Greg Clark calling opponents "nihilistically selfish", while the communities and local government secretary, Eric Pickles, said: "No one should underestimate our determination to win this battle".

Clark later adopted a more conciliatory tone, pledging they were "very happy" to make sure parts of it were "more clearly expressed", citing the definition of sustainable development, among other issues.

Another issue which campaigners wanted to see addressed was more assurance that housebuilding would be targeted at providing more affordable homes.