The only way to determine whether radon levels within your premises are high is to measure the concentrations in the air. Once this has been carried out a risk assessment would be undertaken to determine whether further action is needed. We expect less than 1 in 25 of our workplaces to require action to reduce radon levels, but where this is required, it is usually carried out using standard building techniques.
Radon levels measurements can be obtained using inexpensive dosemeters that you order online and receive through the post. You then site them in areas of your building - usually for 3 months. The Health Protection Agency website, www.hpa.org.uk contains up to date details of validated laboratories that supply such dosemeters, practical information on locating dosemeters and carrying remedial action can also be found at the Health and Safety Executive website, www.hse.gov.uk.
On measuring, if the level shows radon levels below 400Bq/m³ then the only further action required is to decide when the risk assessment will be reviewed. In occupied workplaces where the level exceeds 400Bq/m³, the employer may need to take immediate steps to manage occupational exposures to reduce the radon levels. A specialist radon advisor would then be able to advise on the most appropriate remedial action.