The number of elderly people with dementia is set to soar - but social services will be unable to cope, a charity has warned.
Elderly people face a 'lottery of care'
Friends of the Elderly looked at existing provision in South East England - which has a particularly high concentration of people aged over 65.
The charity found many authorities do not have the necessary information about future need in their areas.
It says action is needed to avoid a "catastrophe in care provision".
Friends of the Elderly said that as the population ages, with increasing numbers of pensioners, cases of dementia, depression and physical disability will grow.
It estimates the numbers aged 85 and over will rise from 1.1m now to 3.3m in 2046 - with the sharpest increase over the next decade.
They warned services would be stretched "to the limit and probably beyond" in the future because of funding shortages.
They say the worst affected places are likely to be large unitary authorities, especially south coast cities where there is a higher concentration of people aged 85 and over, who have a greater risk of developing dementia.
The report, commissioned by the charity from the Institute of Public Care at Oxford Brookes University, looked at 26 local authorities.
It found that many lacked reliable information which they need to plan for future provision in their area.
All said they had a commitment to providing specialist support, but some were found to have much more developed programmes than others, meaning patients faced a "postcode lottery" in terms of the support they could expect to receive.
The report calls for local authorities to work more closely with voluntary and independent service providers to improve services and target them to individual needs.
Douglas Webb of Friends of the Elderly told the BBC: "The kinds of services we really need are quite simple services, social services in people's homes, but they've got to be provided by specially trained people."
Geoffrey Dennis, chief executive of the charity, said more funding was needed "so that older people with mental health needs can receive the services that will enable them to live with the dignity and respect that they deserve".
He added: "There is going to be a dramatic increase in the number of older people with dementia in the coming years and so we are calling for a real commitment from the statutory sector to make the compact with voluntary organisations really work.
"Together, with the proper planning and financial support, we can avoid a catastrophe in the care provision for older people with mental health needs."
Jonathan Ellis, of Help The Aged, said: "The chronic under-funding of social care means that care homes, day centres and home services are reaching breaking point. Those in most need of these services are often older people with mental health needs."
He added: "We need an integrated approach by government, local authorities and the voluntary sector in order to make available a comprehensive and flexible range of services to meet the needs of older people."
Clive Evers of the Alzheimer's Society said: "Three quarters of people
in long term care have a form of dementia.
"Nevertheless much long term care provision continues to assume that a 'one size fits all' approach is appropriate for older people with mental health needs."
A Department of Health spokesperson said: "There have been record levels of investment in older people's services - £900 million for services to help promote independence, an extra £1 billion a year by 2006 for social care services and £56 million to end long waits for NHS cataract operations.
"We are of course aware of the projected increases in older people, and the implications in terms of future care needs.
"Local authorities and the NHS locally is best placed to assess local needs, however, our policies are designed to ensure that frail older people receive the care that they need and want."