LGA estimates more than 7,500 affordable homes lost in England due to conversions that do not go through planning system

More than half of all new homes in some areas have been created by allowing developers to convert offices without building any affordable homes, an impact study of the policy has revealed.

Since 2015, 30,575 housing units in England have been converted from offices to flats without having to go through the planning system, in a bid by ministers to boost housing supply. It means there has been a potential loss of more than 7,500 affordable homes, according to the study by the Local Government Association.

Such office to residential conversions under permitted development rules in place since 2013 accounted for 73% of new homes in Stevenage during 2016-17, the LGA said. In Nottingham, Basildon, Newcastle-under-Lyme, Hounslow and Harlow the figure was more than half.

Last year the Guardian revealed plans by the London borough of Barnet to transform its former head office into 254 flats, some of which are to be 40% smaller than a Travelodge bedroom and have been labelled “dog kennels” by critics.

Across England and Wales, 8% of new homes since 2015 were created by the change of use in office buildings. Councils have warned that “office space could dry up as a result, leaving businesses and startups without any premises in which to base themselves”.

Martin Tett, the LGA’s housing spokesman, said: “Permitted development is detrimental to the ability of local communities to shape the area they live in. Planning is not a barrier to housebuilding, and councils are approving nine in 10 planning applications. But it is essential that councils, which are answerable to their residents, have an oversight of local developments to ensure they are good quality and help build prosperous places. The resulting loss of office space can risk hampering local plans to grow economies and attract new businesses and jobs to high streets and town centres.”

The Department for Housing Communities and Local Government defended the policy. “We are determined to build the homes our country needs and permitted development rights play an important role in helping us deliver more properties,” said a spokesman. “We need a mix of dwelling types to meet different housing needs and over 17,500 additional properties were created by converting offices in the year to March 2017.”