PHE-CRCE have published the latest of their really useful reviews of radiation dose in the UK. This publication data for 2010.
It shows that the largest contributor to the average UK dose is 1.3mSv/yr from Radon and Thorium which it describes as “ubiquitous”.
Patient exposure averages 0.44mSv/yr and occupational 0.0004mSv/yr.
The report concludes that the average doses assessed in this period are pretty much the same as was found in 2003.
Some advice on when to check your basements for radon is found in a later CRCE report.