An influx of new residents to Sussex could itself start to threaten the better life they seek.

If the trend of people to moving south for a better life carries on at the current rate, authorities will be left with only two options: Bury the countryside under a swathe of concrete or go high-rise.

That is the prediction of economic researchers and those tracking social policy in the light of figures which show how the populations of many counties in the UK are shrinking while there are more people moving into East and West Sussex than there are leaving.

This region was shown to be one of most attractive places in the UK to settle and showed one of the most significant "positive population balances" in all of the 15 European Union countries.

Experts believe this trend will not only put more pressure on housing demand but could damage the economy as key workers are priced out of the housing market and out of the county.

Low-cost housing is one strategy being considered to ensure we do not lose vital workers on low to middle incomes.

But some experts believe the amount of housing needed to provide for the growing population will inevitably lead to high-rise developments or building on more green belt land.

Most agencies agree that people on lower and middle incomes, many born and bred in the South-East, are finding it increasingly difficult to find affordable places to live here.

It is not just a problem for families desperate for council housing, up to 3,000 of whom face a five-year wait for a home in Brighton and Hove. It is also a problem for many professional people who would traditionally buy a home.

Brighton and Hove City Council wants more housing schemes to include more low-cost homes, such as a unique development planned for Connaught Road, Hove, which is the first in the city to have 40 per cent low-cost housing. It will have an unusual glass tower but no car parking.

The influx of new residents could also put more pressure on authorities to provide services for a growing population but this will be difficult without key workers.

Health trusts have regular strategic meetings to plan for any population shifts and aim to adapt if the population grows.

The new figures show how Surrey and East and West Sussex have the biggest influx of new residents per 1,000 inhabitants across the entire European Union after Flevoland in The Netherlands and east Scotland.

The survey was produced by the EU's statistical office and charts the shifting population due to migration.

A spokesman for the city council said: "It's highly unlikely Brighton and Hove will be in any position to accommodate large numbers of people over and above the current total of about 250,000.

"We will continue working with housing associations to provide affordable housing as best we can.

"Schools are not such a problem. We have a surplus of primary places. There's a slight shortage of secondary places but that's likely to reduce over the next few years because of demographics."

According to figures from the South-East England Development Agency (Seeda), unemployment in Brighton and Hove continues to fall. But it predicts relatively low wages compared to the high cost of housing may begin to make it difficult for businesses to retain staff.

Brighton and Hove city councillor Pat Murphy, who was lead councillor on housing until the post was abolished, warned: "It could encourage the professional people who underpin the economy to move away. People move here because it's a tolerant place and it celebrates diversity. But there should be a national strategy for local authorities to help each other out across England and tackle the problems of housing and shifting populations."

Coun Murphy also said the Government had to stop the right-to-buy scheme, allowing council tenants to purchase their properties, because this was taking away essential rented homes.

The National Housing Federation said its surveys showed how a household would have to earn an average of more than £41,000 to afford any property in East or West Sussex, including Brighton and Hove. It said the figures made stark reading considering the latest Government figures showed more than 70 per cent of households had incomes below £30,000.

The federation agreed essential services were being put at risk as key workers could no longer afford to live in high value areas such as the South-East.

It has called for further investment in housing and said demand for a new Government-backed £250 million starter home initiative, aimed at helping 10,000 key workers meet the cost of a home, was likely to far outstrip supply. It said subsidised renting schemes in the South-East needed to be added to the initiative.

James Tickell, deputy chief executive of the National Housing Federation, said: "Whilst the starter home initiative is welcome, we fear it may be crippled by a demand that it simply can't meet. Without a considerable drop in house prices there has to be further Government investment in affordable homes."

Housing shortages are only one problem facing the population.

The influx also puts pressure on businesses which are already finding it difficult to keep up with the demand for higher salaries earned by those at the higher end of the earning scale.

Sussex Enterprise is particularly concerned about the impact on the economy. The agency's economic researcher, Joe Clease, said: "If people on lower and middle incomes have to live in cheaper places, even within the county, we are going to have to look not only at where they can live but on how they travel to work."

Mr Clease said the majority of migrants to the South-East were graduates who were pushing up house prices at the expense of those on lower incomes, even though they were just as vital to the economic success of the county.

He said affordable housing was needed but the amount of housing needed to meet demand could change the face of Brighton and Hove and the Sussex countryside forever.

He warned: "If people continue to move here, then authorities will have no option other than build on the green belt or go high-rise."