This is a devolved matter and the information provided therefore relates to England only.
Working with water companies, the Environment Agency has concluded a programme to install Event Duration Monitors (EDM) on the vast majority of storm overflows, just over 80% of overflows in England, by the end of 2020. These monitors provide a robust and consistent way of monitoring how often and for how long storm overflows are used and underpin the Environment Agency's planning, compliance and enforcement work. By the end of 2023, the remaining number will be monitored to provide a complete picture of permitted storm overflows in England.
The EDM data is not yet available for 2021 but the 2020 data is published on gov.uk and can be found by following this link: Defra Data Services Platform.