RR began design work on the SMR c. 2015 with a team of about 150 people, with decisions made near the start of the project to use light water[a] as both coolant and moderator.

Existing nuclear sites including Bradwell, Hartlepool, Heysham, Oldbury, Sizewell, Sellafield and Wylfa were stated to be possibilities.

[6] In 2018, the UK SMR industry sought billions of pounds of government support to finance their putative First of a Kind projects.

[7][8] In 2019, the government committed a further £18 million to the development from its Industrial Strategy Challenge Fund, to begin designing the modular system.

[17][14] In October 2022, Rolls-Royce announced that it was exploring eight possible sites in the UK to build the first of three expected factories for parts of the SMR.

[19] In March 2023, Rolls-Royce stated that the current programme funding of £500 million will run out by the end of 2024, and requested negotiations with the UK government to find fresh investment.

[21] In July 2023, Energy Secretary Grant Shapps said he was launching an international competition to select up to four different SMR technologies "to go through to the final design stage", supported by up to £157 million of finance.

As a comparison the estimated cost for the full-size 3.3 GWe Sizewell C nuclear power station was £22 billion, or around £6.7 million per MWe.