Radon is a natural radioactive gas, which enters buildings from the ground. The joint UK Health Security Agency (UKHSA) (formerly Public Health England (PHE)) - British Geological Survey (BGS) digital dataset Radon Potential for Great Britain provides the current definitive map of radon Affected Areas in Great Britain. Exposure to high concentrations increases the risk of lung cancer. UK Health Security Agency (formerly PHE) recommends that radon levels should be reduced in homes where the annual average is at or above 200 becquerels per cubic metre (200 Bq m-3). This is termed the Action Level. The UKHSA defines radon Affected Areas as those with 1% chance or more of a house having a radon concentration at or above the Action Level of 200 Bq m-3. The dataset allows an estimate to be made of the probability that an individual property is at or above the Action Level for radon. This information provides an answer to one of the standard legal enquiries on house purchase in England and Wales, known as CON29 standard Enquiry of Local Authority; 3.13 Radon Gas: Location of the Property in a Radon Affected Area. Radon Potential for Great Britain also provides information on the level of protection required for new buildings as described in the latest Building Research Establishment guidance on radon protective measures for new buildings (Radon: guidance on protective measures for new dwellings; BR 211, 2015 in Scotland, England, Wales and Northern Ireland). This radon potential hazard information for Great Britain is based on UKHSA indoor radon measurements and BGS digital geology information. This product was derived from BGS Geology 50k (formerly known as DigMap50k) version 8 and UKHSA in-house radon measurement data. The indoor radon data is used with the agreement of the UKHSA. Confidentiality of measurement locations is maintained through data management practices. Access to the data is under licence.