Since April 2016, all local authorities in England have been required to prepare ‘Right to Build’ registers of all residents wishing to build homes themselves or explore custom building.
Research published this week by the National Custom and Self Build Association (NaCSBA) suggests more more than 40,000 people have now signed up to these registers.
However, while the figures show the number of people on council self-build registers has more than doubled in two years, registrations have slowed considerably in the last 12 months.
In December 2017, the NaCSBA published research which found 33,000 people had signed up to the registers, up from 18,000 the year before.
The latest figures suggest the number of people on self build registers grew by half as much in 2018 than it did the previous year.
The NaCSBA said the numbers now registered "remain far short of the real underlying demand".
It said councils are increasingly placing restrictions on those joining the registers and, as a result of the difference in attitudes between councils, described the government’s self build policy as a "postcode lottery".
According to the organisation, around one in four councils now has restrictions in place, including charges to join and remain on registers. Many local authorities have also failed to promote registers to local residents, it added.
Michael Holmes, chair at the NaCSBA, said, "While it’s great news that the numbers who want to self build has increased, NaCSBA has deep concerns that, rather than meet the demand for custom and self build homes through the granting of planning permissions to match demand, some local authorities are instead seeking to minimise the number of registrations.
"Through their actions, these local authorities are reducing the number of homes that are built as well as depriving individual and families of the best and most cost-effective route to a well-designed home of real quality and value."
For its study, NaCSBA said it issued a Freedom of Information request to all 336 English planning authorities last month requesting details on the operation of their registers and the numbers of people signed up.
An investigation by Planning earlier this year found councils including the London boroughs of Camden and Islington are charging as much as £350 to residents registering their interest in self build.
Speaking at the Planning for Housing conference in October, Mario Wolf, director of NaCSBA's Right to Build Task Force, warned that high fees were suppressing demand from people wanting to build their own homes.