[en] Body radioactivity in the general public has been measured in 2339 volunteers throughout the U.K. A mobile whole-body monitor visited collaborating Medical Physics Departments and data were also contributed by Medical Physics Departments possessing installed counters. Levels of body radiocaesium ranged from below detection level to 4149 Bq. Radiocaesium levels were normalised by dividing by the content of natural body potassium-40. In all cases, the dose rate to the body from radiocaesium was less than that from potassium-40. Radiocaesium levels were 2-3 times higher in N.W. England, Scotland and N. Wales than the rest of the country, but this factor is much less than the variation in deposition of Chernobyl radiocaesium. This discrepancy may be accounted for by the nationwide distribution of foodstuffs. At all sites where volunteers were monitored, the ratio of caesium-137/caesium-134 was consistent with a radiocaesium intake attributable primarily to fallout from the Chernobyl fire. (author)