The survey, carried out for the European Association for the Study of Obesity, also found that a fifth (20%) of UK adults who consider themselves to be of normal weight are in fact overweight.
This compares with 16% in France and 10% in Italy.
The UK part of the survey was based on 2000 adults who were asked to provide their heiht and weight, from which their BMI (body mass index) was calculated.
Data from these self reports showed that 20% of respondents would be classed as obese and a further 33% would be overweight.
Less than a fifth of UK residents identify obesity as a disease, the lowest proportion in Europe.
Wise, J. (2015) People in UK Under-estimate Their Weight. BMJ 2015;350:h2621.