The map is based on Met Office UKCP18 Climate Projections.
The climate projection data: The data selected is the average July temperature (mean) at the surface using a RCP 8.5 scenario. The climate model is based on the HadGEM3-GC3.05 > r00lilp0000 > HadREM3-GA705 > HadREM3-RAIIM. Local projections at 2.2km resolution are provided for three time periods: 1981-2000; 2021-2040; 2061-2080.
Downloading the data: UKCP18 data can be downloaded from the CEDA website. The specific data is available here. See Table C.1. in accompanying documentation for information about file name conventions.