Overcrowding in homes affects up to 25 times more families than official statistics suggest, the government has warned.
According to the existing standard, which is used by most councils but has not been updated since 1935, only 20,000 households suffer. A modern analysis suggests that 500,000 need more room.
"We've made huge progress in tackling and preventing homelessness but overcrowding is still too often a hidden problem which can have a massive impact on children's lives," the housing minister, Yvette Cooper, told the Guardian. "That's why we need to raise the massively outdated overcrowding standards and why we need to build more family homes for the future."
Under the standards, a one-bedroom flat is suitable for a couple with a teenage boy and teenage girl because the father and son could share one room and the mother or daughter could sleep in the sitting room or kitchen.
But under a modern definition of overcrowding, the same family would be entitled to a three-bedroom flat.
"The definition of overcrowding standards used by many authorities is no longer defensible in a modern society," said a document published by the Department for Communities and Local Government.