I am looking for typical electricity demand profiles with hourly granularity for domestic, commercial and industrial sectors in the UK in the present and, if possible, in the future.
Could you point me relevant sources?
I've recently worked with the European portal for electricity transparency https://transparency.entsoe.eu/.
Probably you can find some answers over there. There is an API which needs a simple registration but it's free and produces time series in XML format.
It may take some time to get an overview of the different categories but I could imagine e.g. Total Load Forecast - Year Ahead to suit your needs.