The number of people with dementia in Sussex is expected to rise by more than 7,000 over the next 15 years.

Research published by the Alzheimer's Society shows cases of the disease in some parts of the county are expected to go up by as much as 30 per cent.

The charity says the results have sparked fears that health and social services may find it difficult to cope as demand goes up among an increasingly older population.

Around 9,893 people are living with Alzheimer's in East Sussex at the moment but the figure is expected to increase to around 13,020 by 2021.

In West Sussex the number is expected to rise from 12,658 to 16,692.

Both counties have pockets of areas where there is a large concentration of elderly people who are more vulnerable to developing the disease.

However Brighton and Hove slightly bucks the trend by showing an expected small drop in cases from 3,196 now to 3,076 in 2021.

The study was carried out by the London School of Economics and King's College London on behalf of the charity and found dementia affects around 116,000 people in the South East, including London.

Charity South East regional director Mary Garvey said: "Dementia is set to dramatically increase in the South East yet it is unclear how our health and social services plan to deal with dementia now and in the future.

"The report clearly shows the scale of dementia in the region and predicts the number will grow by more than 27,000 people by 2021.

"Dementia must become a local and national priority and we need leadership from local authorities and services to develop plans to respond to the challenge."

The Sussex Partnership NHS Trust, which provides mental health services for older people across the county, says a lot of work is already being carried out to plan for the future.

Associate director for older people's mental health services in West Sussex, David Howell, said: "We are working on an investment strategy for the future, which mirrors the growth in the population of older people.

"We want to ensure that the services we provide grow with the demand.

"The trust has already invested in new community based services, which will help reduce dependence on specialist in patient bed based provision.

"This means we can provide more individually tailored packages of care, aiming to treat people suffering from dementia in their own homes.

"Only those people who really need inpatient care will go into hospital. Hospital services will be specifically designed to meet the needs of these vulnerable patients."