But a survey of some of the lowest earners in the country shows the nutritional value of what they eat is little different to everyone else.

In fact, the same deficiencies in diet were shared by all the population and the findings suggest that poor eating choices are far more widespread than previously suspected - affecting many wealthier families.

These included low fruit and vegetable consumption, not eating enough oily fish and eating too much saturated fat and sugar.

'This is a large and significant study and it shows we are all eating just as bad a diet as each other,' said Tim Lang, professor of food policy at City University.

The poorest families were eating only slightly more sugar and slightly less fruit and vegetables, according to the study of 3,728 respondents in the bottom 15 per cent of the population in terms of what the Food Standards Agency described as 'material deprivation'.

Alison Tedstone, head of nutritional science at the FSA, said: 'Overall, people on low incomes have less than ideal diets, but their diets are only slightly worse than those of the rest of the population.'

The study also showed that low earners are choosing to eat unhealthily. Their food choices were not linked to their income, their access to shops or their cooking skills, said the FSA.

The findings appear to contradict assumptions that the poor cannot afford healthier foods or are too far away from shops that sell them.

The Low Income Nutrition and Diet Survey showed that like the rest of the population, the poor's daily fruit and vegetable intake on average is below the recommended five portions. Fewer than 10 per cent of respondents hit this target, while around 20 per cent ate less than a portion per day.

More than three quarters (76 per cent) of men and 81 per cent of women did less than one 30-minute session of moderate or vigorous exercise per week.

Some 45 per cent of men and 40 per cent of women were smokers.

This compares with 28 per cent of men and 24 per cent of women in the general population.