The Environment Agency says....

"We will not authorise any disposals unless are satisfied that public
radiation exposures are below a ‘dose constraint’ of 0.3 millisieverts
(mSv2) per year. In most cases we would expect them to be no greater
than 0.02 mSv per year (average UK doses from all sources, including
natural background and medical exposures are about 2.6 mSv per year)."

http://www.environment-agency.gov.uk/business/sectors/100241.aspx