Applications to build an additional 35,000 homes on green belt land were submitted last year, taking the total number proposed for construction on protected land to a record 460,000.

New data from the Campaign to Protect Rural England (CPRE) released on Monday showed that more than 24,000 homes were constructed in the UK’s green belts in the past nine years. Its State of the Green Belt 2018 report reveals that the number of finished homes constructed on the protected areas almost doubled last year to about 8,000.

The government has pledged to protect green belt land but housing campaigners believe much more controlled land could be released to build badly needed affordable new homes.

Most of the construction to date has been on brownfield sites within the green belt, but the data suggests that the vast majority of homes constructed on greenfield green belt land is in higher price brackets unattainable to most buyers. Only 27% of homes built or approved on greenfield land since 2009 fitted the government’s definition of affordable housing.

The CRPE data, collated from various sources, came just weeks after the government’s revised national planning policy framework, issued last month after a consultation period in the spring. The new framework, released with a slew of other announcements just before the parliamentary recess, contained a number of crucial policy points.

In the new policy, ministers overruled campaigners, parish councils and others who called for a blanket ban on building in the green belt, while also not agreeing to the further relaxation of the green belt rules sought by developers. The government concluded: “The restrictions on the location of housing in the green belt are in place to prevent gradual erosion of green belt boundaries over time and to maintain openness. The revised framework does however continue to make clear that plans may provide for limited affordable housing for local community needs.”

The CPRE found that in 2017-18, more than 8,000 homes were built on the green belt, with 4,800 on brownfield sites and 3,300 on previously undeveloped land. That compares with more than 4,000 completions in 2016-17, of which fewer than 1,000 were on greenfield sites.

The developments represent only a tiny proportion of the land currently held as green belt in the UK. The 315 hectares built on last year make up only 0.002% of the UK’s 1.6m hectares of green belt.

Matthew O’Connell, housing adviser at the Country Land and Business Association, which represents the owners and managers of more than 10m acres of rural land, said the green belt was a planning designation intended to prevent urban sprawl, rather than a policy to protect beautiful countryside. He said: “Despite the acute need for new homes, the green belt reduced by less than 0.05% between 2016-17 and it still covers a greater area than developed land in England.”

Sarah Lee, the head of policy at the Countryside Alliance, said some land should be removed from green belt, with stricter rules on the remainder. “The [report] just demonstrates how we need a real review of green belt policy to make sure it is fit for purpose and properly protects communities and landscapes where it is needed. That means you would be unable to build on green belt, but would equally mean some land currently classed as green belt would be available to deliver the much-needed affordable housing in the countryside.”

Robert Colvile, the director of the Centre for Policy Studies, said the current system was flawed. “It is bizarre that greater London is surrounded by an area three times larger on which little can be built, irrespective of the quality of the land,” he said. “No one is calling for the green belt to be concreted over. But there is plenty of scope for judicious development, for example around transport hubs, while protecting the most beautiful countryside.”

CPRE said the “exceptional circumstances” rules for green belt building should be strengthened to ensure any proposals for development must pass strict tests.

The Green party called for a land value tax to encourage the use of vacant land. Currently, thousands of hectares of land that have been approved for homebuilding goes unused as the owners wait for values to increase rather than construct housing. A land value tax would penalise landowners who sit on land for which building permits have been issued.

The party’s co-leader Jonathan Bartley said: “Instead of overseeing the erosion of our green space, the government should invest in increasing social and affordable housing on the plentiful brownfield sites in our towns and cities, take action on empty homes, and introduce a land value tax to encourage the use of vacant land and reduce speculation.”