About a tenth of new flats completed since 2015 were converted from offices, government data has revealed.
Of the 347,510 new builds recorded between 2015-16 and 2016-17, 30,575 were office to residential conversions.
Campaigners warn these conversions have led to a greater strain on the affordable housing market because councils have no means of stipulating what proportion of such developments has to be affordable.
The Local Government Association said office conversions were “detrimental” to local communities.
“It is vital that councils and local communities have a voice in the planning process,” said Martin Tett (Con), the LGA’s housing spokesperson.
“At present, permitted development rules allow developers to bypass local influence and convert offices to flats, and to do so without providing affordable housing and local services and infrastructure such as roads and schools.”
Since 2015, office to residential conversions have not required planning permission, meaning that developers have been able to bypass regulation and local scrutiny.
Daniel Frisby, senior planner at law firm DMH Stallard, said: “As well as this policy having no provision for councils to require the delivery of affordable housing, it also fails to enforce appropriate minimum space standards.
“In our experience this leads to extremely poor living accommodation with some units being as small as 15 m2 [less than half the standard advised floorspace for one-bedroom flats],” he added.
LGA analysis found that had councils been able to stipulate 25% of homes were affordable, an additional 7,644 affordable homes could have been provided over the two-year period.
The government defines affordable housing as “social rented, affordable rented and intermediate housing, provided to eligible households whose needs are not met by the market”. Rents are subject to controls limited to “no more than 80 per cent” of the local market rent.
The numbers of conversions also differs according to region - leading to a national disparity, the local data shows.
The council areas with the highest proportions of new homes that were converted from offices are Stevenage BC, where almost three-quarters of units fell into this category in 2016-17; Three Rivers DC, with 64% and Sutton LBC with 61%.