Researchers from Bristol University found there were high death rates in areas of shrinking population.

They used the standardised mortality ratio, which compares the number of deaths observed in a population with a baseline average set at 100. A score of 130 denotes a death rate 30% higher than the national average.

People were likely to leave areas en masse because of socio-economic factors such as low employment, high crime rates, poor housing and poor health care.

All these have been implicated as causes of bad health.

The findings were published in The Lancet medical journal.

Escape from deprivation

Only those who were relatively well off could afford to move out of such areas, while poorer people had to stay put and endure the conditions, according to one of the researchers.

Rundown areas provoke an exodus

Dr Mary Shaw compared the situation to that on the deck of the doomed Titanic.

She said: "During the sinking of the ship the first class passengers were more likely to survive than the rest.

"This was not because they were fitter and stronger, but because their social position meant that they were located on higher decks and had better access to lifeboats.

"The third class passengers, on the other hand, were less likely to survive because their access to these was more limited."

Higher than average death rate

The research showed people living in areas where population had decreased by a fifth or more since 1971 had a 25% greater chance of dying than the national average.

In many areas population was falling as people who could afford to move fled to places with better employment prospects and services, more amenities and higher wages.

Dr Shaw said: "Middle class people who are better off and more highly educated than their working class counterparts are more likely to migrate out of less desirable areas.

"If they perceive that an area is deprived, has poor services and poor schools, for example, they will, if they are able, move to an area where high quality forms of these facilities are more freely available and accessible.

"Others may very well want to move to a 'better' area, but they may not be able to do so. This differential migration seems to be a driving force behind increasing mortality by area."

The places people moved from often suffered from the very fact that their populations were reduced, the researchers found.

Shops close as population plummets

Shops closed, schools were forced to merge and reduced local demand affected local employment.

Top of the shrinking population league was Salford, Greater Manchester, where the number of residents had declined by 34.4% between 1971 and 1991.

Salford had a mortality rate 30.5% higher than the national average - the second highest in a table of 20 towns and cities outside London.

The city of Glasgow had the second steepest population decline (32.7%) and the highest mortality rate (30.8% above the national average).

Health targets

The researchers said since funding for local and health services was mainly allocated by head of population, some of the most deprived areas had also seen some of the largest cuts.

They said Health Action Zones - the latest government initiative to tackle such problems - would not reverse the trend.

A Department of Health spokesman said this remained to be seen and he said the research demonstrated the need for the recent public health green paper.

He said: "It's concerned with making sure that people have access to decent shops and that children in schools have reasonable diets.