Following the Japanese Cool Biz campaign which advocated relaxed dress codes and cooling set-points of 28 degrees C in air-conditioned public buildings, other countries have introduced similar policies, with temperature limits varying in different countries. In the UK the British Council for Offices suggested that the summer cooling set-points of UK air-conditioned offices should be increased by 2 degrees C from the previously recommended 22 +/- 2 degrees C. However, these recommendations are largely supported by desk-based analysis rather than using field studies. This paper presents the findings of a blind, controlled intervention study conducted in the summer of 2010 in an office building in London to investigate the effects of increasing the current cooling set-point to 24 degrees C. The temperature of one floor was changed and compared with a 'control' floor where the set-point remained unchanged. The indoor air temperatures were measured at various locations across the floors to monitor the temperatures the occupants were experiencing. The BUS post-occupancy evaluation survey was used to assess occupants' self-reported comfort and satisfaction, whilst the NEP questionnaire was used to estimate occupants' environmental attitudes. The findings from statistical analyses of the data collected for all 129 participants suggest that increasing the set-point temperature led to the occupants feeling significantly warmer in comparison with the group at lower temperature settings. Nevertheless, this did not affect the self-reported thermal comfort of the occupants in the intervention group, as depicted by an insignificant difference between the two groups. It was also observed that there is a positive correlation between the occupants' tolerance of higher indoor air temperatures and their environmental attitudes, indicating that this could play a key role in the acceptance of indoor temperature changes in the UK. (C) 2012 Elsevier Ltd. All rights reserved.