London mayor Boris Johnson is set to backtrack from a threat to ban all new homes from having windows in only one wall after uproar from housebuilders over the impact on build costs

Last summer Johnson issued a consultation on space standards for new homes that included plans to outlaw “single aspect” housing through the planning system, in order to stop the construction of tiny flats he called “hobbit homes”.

A study by consultants Savills and EC Harris said Johnson’s standard could cost builders £37,500 a unit, because of changes it would force to layouts, thereby making many sites unviable.

Building understands the final policy, earmarked for release in June, will allow the construction of single aspect housing in most circumstances.

Yolande Barnes, director of research at Savills, said: “This move is welcome. Some have said it could have made 50% of London sites undevelopable; some sites would have been completely scuppered.”