Plans to build thousands of homes on Green Belt land in North Herts and Stevenage will do nothing to help ease the affordable housing crisis, campaigners have warned.

The Campaign for the Protection of Rural England says the public are being “sold a lie” by developers keen to “gobble up” protected Green Belt land to build homes that will be unaffordable to those most in need of them.

The group has reviewed local plans from across England for its annual State of the Green Belt report.

According to this study, local authorities are planning to allow almost 460,000 homes to be built on the country’s Green Belt to help meet their housing targets.

In North Hertfordshire, the CPRE has identified plans to build 13,335 homes on Green Belt land – with Green Belt within the Stevenage authority boundaries earmarked for another 1,350.

This land is part of the wider Metropolitan Green Belt, across which 156,030 homes are expected to be built.

However, the CPRE says that there are enough brownfield sites – land which has been built on before – to build a minimum of 3,976 homes in Stevenage and 1,206 in North Herts. They argue these should be prioritised over Green Belt developments.

All the brownfield homes in North Herts, and at least 1,233 of those in Stevenage, could be built within the next five years.

Tom Fyans, director of campaigns and policy at CPRE, says Green Belt land is being “eroded at an alarming rate” across the country.

Far from providing the solution to the affordable housing crisis, he continued, building on Green Belt land is serving only to further “entrench the issue”.

If local affordable housing targets are applied to Green Belt developments in North Hertfordshire, only 40 per cent would meet the government’s definition of affordable. In Stevenage, it would be 25 per cent.

But the CPRE’s analysis shows that there is often a gap between planning targets and what is actually approved by local authorities.

The average target across local authorities in England is for 31 per cent of new homes to be affordable.

According to the CPRE, though, only 22 per cent of housing units that currently have planning permission meet the definition of affordable.

On greenfield sites, which is land that has never been built on before, the figure is 27 per cent.

England’s Green Belt areas, which cover approximately 13 per cent of the country, were established with the aim of stopping urban areas encroaching too far into the countryside.

Local authorities can propose to release land from the Green Belt entirely in “exceptional circumstances”, or otherwise approve developments in “very special circumstances”.

However, the CPRE says that both these bars are currently “set too low”.

Since 2009-10, plans for around 207,000 homes on England’s Green Belt land have been submitted.

Just under 65,000 have been approved, while around 105,000 of them have yet to be decided.

The CPRE is now calling on the government to address the affordable housing crisis with “increasing urgency” by instead prioritising development on brownfield sites.

Mr Fyans said: “The government is failing in its commitment to protect the Green Belt.

“It is essential, if the Green Belt is to fulfil its main purposes and provide 30 million of us with access to the benefits of the countryside, that the redevelopment of brownfield land is prioritised, and Green Belt protection strengthened.”

A spokesman for the Ministry of Housing, Communities and Local Government said: “We are clear that building the homes our country needs does not mean tearing up our countryside.

“Last year the number of new homes built was the highest in a decade, and only 0.02 per cent of the Green Belt was developed for residential use.

“We are adding more certainty to the planning system and our new planning rulebook strengthens national protections for the Green Belt, and says that councils may only alter boundaries in exceptional circumstances once they have looked at all other options.”