The European Smart Grids Task Force Expert Group 3 has authored an insightful report on the deployment of demand side flexibility and the specific case of explicit demand response in Europe.
The report is called Demand Side Flexibility. Perceived barriers and proposed recommendations and can be accessed through the European Commission website:
https://ec.europa.eu/energy/sites/ener/files/documents/eg3_final_report_demand_side_flexiblity_2019.04.15.pdf