The Food Standards Agency's findings contradict the assumption that low earners have a significantly worse diet. But its study of nearly 4,000 low income respondents revealed high levels of obesity and low levels of exercise.

The respondents' diet choices were not linked to their income, their access to food stores nor their cooking skills, the FSA said. Instead, consumers in the group were simply choosing not to eat as healthily as they should, the watchdog found.

Overall, they had higher levels of smoking and alcohol consumption and lower levels of physical activity than the population as a whole.

The Low Income Nutrition and Diet Survey studied the dietary habits of 3,728 people who were in the bottom 15% of the population in terms of material deprivation.

The respondents' diet-related problems were similar to those of the wider population. Those included low fruit and vegetable consumption, not eating enough oily fish and eating too much saturated fat and sugar. Obesity levels were also "very high" - in line with the population as a whole.

Some differences did emerge between the diets of low earners and the rest of the population. People on low incomes were less likely to eat wholemeal bread.

On average, they drank more sugary soft drinks and whole milk, and ate more table sugar. The group was also more likely to eat more processed meat.

Like the rest of the population, their daily fruit and vegetable intake on average was below the recommended five portions.

In a foreword to the study, FSA chair Dame Deirdre Hutton said: "The report highlights areas of concern for the low income population which are, in many respects, similar to those already identified in the general population although often to a greater degree."