PLANNING rules lowering requirements for affordable housing provision will lead to a rural housing crisis, say England's national park chiefs.

England's ten National Parks expressed their concern in an open letter to communities secretary Eric Pickles before Christmas.

The parks are concerned that new rules unveiled by the government put their ability to achieve more affordable housing at risk.

It follows a government consultation last year proposing a threshold of ten units below which local planning authorities would not be able to require a proportion of new housing to be affordable.

In National Parks, most sites for development tend to be small, infill opportunities and conversions for new affordable housing development.

The introduction of any threshold - even one lower than ten units - risked "seriously threatening our ability to facilitate affordable housing in National Parks for local needs," said the letter, which can be downloaded here.

Jim Bailey, chairman of National Parks England, warned: "These changes go to the heart of how we can respond to the need for affordable housing in our rural communities."

Communities minister Brandon Lewis later announced the removal of Section 106 agreements from sites of fewer than 10 homes in a written statement to parliament.

It means developers will no longer have to provide affordable housing when building homes on smaller sites.

For designated rural areas under section 157 of the Housing Act 1985 - which includes National Parks and Areas of Outstanding Natural Beauty - authorities may choose to implement a lower threshold of five units or less, beneath which affordable housing and tariff style contributions should not be sought.

This will also apply to all residential annexes and extensions.

Mr Lewis said: "Within these designated areas, if the 5-unit threshold is implemented then payment of affordable housing and tariff style contributions on developments of between 6 to 10 units should also be sought as a cash payment only and be commuted until after completion of units within the development.

"These changes in national planning policy will not apply to rural exception sites which, subject to the local area demonstrating sufficient need, remain available to support the delivery of affordable homes for local people."

The Rural Services Network believes abandoning the requirement for developers to include affordable housing when building homes on smaller development sites was poorly thought through.

Rural Services Network housing spokesman Andy Dean said: "This decision is huge blow for rural communities. It is very, very disappointing news."