The departing prime minister wants her successor to introduce mandatory universal regulations to provide clear national standards.
“I cannot defend a system in which owners and tenants are forced to accept tiny homes with inadequate storage… Where developers feel the need to fill show homes with deceptively small furniture… And where the lack of universal standards encourages a race to the bottom,” she said.
Currently, some local authorities make Nationally Described Space Standards a condition of granting planning permission. But many do not - and even where standards are applied, they are not mandatory.
Mrs May says that this has resulted in different rules in different parts of the country, leaving “tenants and buyers facing a postcode lottery.”
Addressing the Chartered Institute of Housing conference, she is also expected to set out next steps on the social housing green paper agenda, with an action plan expected in September.
However, builders said they were not to blame for the size of their houses. Local authorities who did not mandate space standards within local planning must take their share of the blame, they said and the Government knew this was happening and did not take the right steps to solve it.
Richard Beresford, chief executive of the National Federation of Builders (NFB), said: “The issue of tiny homes has been raised over and over again. The government kicked it into the long grass and it is disingenuous of the prime minister to make it a priority, now that she is stepping down.”
Rico Wojtulewicz, head of housing and planning policy at the House Builders Association, said: “I’ve lost track of the number of times I raised this issue with the Government and councils. We can ensure larger homes are built through tools such as space standards, but councils must also know the types and size of homes that are being built. That requires the Government to begin publishing those statistics once again.”