The main design built at the site was the demonstration steam-generating heavy water reactor (SGHWR) providing power to the National Grid.

John Cockcroft, in charge of the Research Group, immediately began pressing for a new site to be set aside for the construction of multiple experimental reactors, with the aim being to try many designs in order to develop the best possible commercial systems.

This was opposed by Christopher Hinton, of the Industrial Group, who wanted to pick a single design and focus their energies on that.

The AEA were granted planning permission for the development by Dorset County Council, which was confirmed by a public inquiry, but during the process it was discovered that various rights of common may have existed over the land.

In order to enable the development to go ahead as quickly as possible, the government introduced, and Parliament passed, the Winfrith Heath Act 1957, extinguishing any rights of common over the land, and allowing for a compensation process for any commoners whose rights had been extinguished.

The Durley Hall Hotel at Branksome Chine was bought in 1958 for single staff and temporary accommodation.

[3] Cockcroft also suggested that larger fusion reactors be built at Winfrith, but this was met by serious pushback from the scientists involved in the programme.

In 1995 the eastern part of the site became the Winfrith Technology Centre, and 218 acres on the western side were decommissioned.

[13] The core consisted of a bank of metal pressure tubes (zirconium alloy) which passed through vertical tubes in a tank of heavy water moderator – allowing the designers to do without the pressure vessel that normally contained the reactor's core.

[4] It began operating in 1967,[15] and was notable for being built within the allotted timescale (four years), and for being under-budget.