The Central Electricity Generating Board carries out routine high resolution gamma scanning measurements on fuel discharged from civil advanced gas-cooled reactors in its postirradiation facility at the Atomic Energy Establishment, Winfrith. The measurements yield thermal power density distributions within fuel channels to accuracies of within ±2%, which are used to check the corresponding theoretical predictions and assist the interpretation of postirradiation data. The high precision is achieved by careful attention to detail in both the measurement of fission product count rates and the subsequent analysis, and is demonstrated by internal consistency checks and comparisons with results of independent methods.