Interesting, publicly available Solar data available online form SOLARGIS
High level data maps here >> https://solargis.com/maps-and-gis-data/download/united-kingdom
The maps and data for United Kingdom have been released in parallel with Global Solar Atlas, which is published by the World Bank Group, funded by ESMAP, and prepared by Solargis. All maps on this page are licensed by The World Bank under the Creative Commons Attribution license (CC BY 4.0) with the mandatory and binding addition presented in Global Solar Atlas terms. You are free to download, share, adapt, use the maps but you must give appropriate attribution:
© 2020 The World Bank, Source: Global Solar Atlas 2.0, Solar resource data: Solargis.