Since 1951, the average waist size has grown by 6.8 inches to 34.4 inches.
The survey found that since the average bust has gone up by 2 inches to 39 inches and hip size has shot up by 2inches to 41 inches, on an average, women are 10 pounds heavier.
The survey conducted by at University College London researchers that included 9,000 men and women found that even men have had a similar experience.
Brit men are fatter around the waist on an average of 7 inches and heavier by 18 pounds, as compared to what they ere during post-wars.
Over the past 12 years, the proportion of children aged two to ten and classified as obese has jumped from less than 10 per cent to almost 17.
"If that trend continues, by mid-century we'd be getting close to half of all children classified as obese," the Daily Mail quoted Ed Balls, Secretary of State for Children, Schools and Families, as saying.
"It's clearly important that we act," he added.
The rapid change in shape and weight has been attributed to a more sedentary lifestyle and high calorie intake.
"We are tending to say, 'This patient has a hyper-appetite problem' rather than maybe, 'They are eating too much'," Dr Hamish Meldrum said.
However, there is some relief for Britons, for Americans take the lead as the fattest nation in the developing world.
According to the UCL study, British women are an average of 3 pounds lighter and 0.4in slimmer than their U.S. counterparts. British men are 12lb lighter and 1.1in thinner than the average American.