Browsing instead? Development land by county and city region totals the registers across a whole area; every English council’s register has the site counts and dwelling capacity one authority at a time.
Enter a town. The app pulls council Brownfield Land Register sites (previously-developed land flagged as suitable for development) from planning.data.gov.uk, ranks them by size, planning status, deliverable flag and arterial frontage minus green-belt / flood / listed / conservation constraints, and maps them.