Not especially - We are at the top of the European leader board by this data
http://miscellanea.wellingtongrey.net/2007/05/06/global-obesity-fatness-by-country/
But only by 1%
Australia and NZ come running up behind - not countries you normally associate with Obesity.
Of course that data is taking obesity with a BMI over 30
On that basis I'm obese! ( I must be one on the fittest obese people about)
If instead you look at what the average BMI is rather than the number of people over a limit you get a slightly different story
http://news.bbc.co.uk/1/hi/health/6148456.stm
Now we are 10'th in the league
So it seems that Britain is more a nation of people who really could stand to lose a few pounds overall but with fewer grossly obese people