The government will today publish long-awaited reforms to the planning system which have been the focus of a bitter dispute with countryside campaigners.

Last summer ministers unveiled their proposals for slimming-down more than 1,000 pages of policy on planning rules into a 50-page "national planning policy framework", which they said would boost growth while protecting the environment.

The plans, which centre on a "presumption in favour of sustainable development", have been opposed by conservation and countryside groups such as the National Trust amid fears they would lead to a return to urban sprawl.

In the run-up to the publication of the reforms, there were reports that the new planning rules could be exploited to build up to 100,000 homes in the green belt near the new high speed line to Birmingham, as part of a huge housing expansion.

Announcing when the reforms would be published during his Budget speech last week, Chancellor George Osborne confirmed the pro-growth agenda driving the move, saying the "presumption in favour of sustainable development" would stay.

He insisted the changes would be the biggest reduction in business red tape ever undertaken, as he claimed there were specific examples of companies taking their business - and jobs - to other countries because of England's planning rules.

Osborne also said the final policy would protect England's "most precious environments", prompting immediate concerns that countryside that is not protected by designations such as green belt or national parks will be at increased risk.

Ahead of the publication of the document, the Campaign to Protect Rural England (CPRE) also warned protection for green belt land could be unintentionally weakened by the new policy.

It raised concerns the definition of "sustainable development" was too vague to govern planning policy in the draft proposals and local plans, which set out what development councils want in their area, could give way to a "free for all".

The CPRE said it feared the planning reforms would not deliver enough affordable homes - one of the key benefits supporters of the changes say it will provide.

The Countryside Alliance said local people in the countryside wanted affordable housing and for rural businesses to be able to expand - and that they were the best placed to decide what development was appropriate and what should be opposed.

Barney White-Spunner, executive chairman of the Countryside Alliance, said the first draft of the reforms had been too vague on giving power to communities, and hoped that the government had listened to local concerns before the final reforms.

He added: "At a time when rural pubs, shops and schools are closing at a worrying rate, a more simple but rigorous set of planning regulations could go a long way to reviving the struggling rural economy."