I couldn't find a breakdown of open sided vs enclosed but I did find proposals for updating rules for EVs in enclosed Car Parks https://assets.publishing.service.gov.uk/media/5c7e3f75e5274a3b7de3b294/WS_4_DCLG_BD_2887__D26V1__286858_Final_work_stream_4_report. pdf
Note again this is only enclosed car parks or open car parks whose structure is supporting another building.