Hundreds of thousands of older people and their families are being forced to pay a "dementia tax" if they are struck down by the condition, a leading charity has warned.

People with dementia are having to fork out for care while people with other long-term conditions are being looked after by the state, the Alzheimer's Society said.

Sufferers and their families are paying as much as £21,000 a year in covering the costs of social care and unpaid care provided by families and friends, experts estimated.

Overall, researchers have calculated that the cost of dementia to the UK - through health and social care costs - has hit £26 billion a year. But people with the condition, their carers and families shoulder two-thirds of the cost - approximately £17.4 billion annually.

The charity said people are being forced to pay a "dementia tax" whereby they have paid tax all their working lives contributing towards the NHS but when they become ill in later life they are paying out again to cover costs of care.

"We have this division between health and social care and that people with dementia are at the forefront of the inequity that comes as a result of that," said Alzheimer's Society chief executive Jeremy Hughes.

 "If you have another disease, like cancer or heart disease, you actually get all your treatment on the NHS. If you have dementia, where there is no medical intervention that cures you or treats you other than ameliorates the condition at best, most of the support you need comes from social care and most of that comes from the individual family and the family carers or from a severely strapped social care system.

"The dementia tax - whereby people pay their taxes when they are working to pay the NHS but when they need support for dementia they have to pay again because the support they need isn't on the NHS - is alive and influencing the livelihoods of hundreds of thousands of people."

The charity is urging the Government to end the "artificial divide" between the health and social care systems, which it says "unfairly disadvantages" people with dementia.

The comments come as the charity published two reports into the prevalence and costs of the condition.

The reports, from experts at the London School of Economics (LSE) and King's College London, found that 225,000 people in the UK develop the condition every year - or one person every three minutes.

They estimated that there will be 850,000 people affected by the condition by next year. This figure is expected to soar to two million by 2051, they said.

Meanwhile, experts also analysed the costs of the condition and found that sufferers across the UK and their families are paying out £5.8 billion for social care. And the 1.3 billion hours of unpaid care provided by friends and family would cost the state £11.6 billion if it was not provided by this support network for free, they said.

LSE professor of social policy Martin Knapp said many people with dementia and their families are essentially paying out £21,000 a year through the unpaid care provided by carers and covering the costs of social care.

Mr Hughes said: "This new research exposes the staggering financial and human impact of dementia. It is plain to see that our social care system is on its knees, leaving an army of tens of thousands of unpaid carers bearing the brunt.

"If you have cancer or heart disease, you can quite rightly expect that the care you need will be free. That is just not the case for people with dementia. Families are forced to break the bank to pay for basic care for a loved one.

"These spiralling costs cannot continue unchecked. 225,000 people develop dementia in the UK every year - that is one every three minutes.

"While government has woken up to the challenge dementia presents, today's report reveals we need radical solutions and serious funding commitments to put social care on a sustainable footing."

The charity has also called for an improvement in diagnosis rates and said no one should wait longer than 12 weeks from seeing a GP to receiving a diagnosis.

Mr Hughes added: "While in recent years there has been a small improvement in dementia diagnosis rates, a postcode lottery still prevails. Everyone with dementia should have access to the certainty of a diagnosis and the right support to come to terms with, and manage, the condition."

Health Secretary Jeremy Hunt said: "I want to make sure those with dementia, their families and carers get the help they need. It's precisely because people face such unfair care costs that we are transforming the way people pay for care, capping the amount they have to pay and providing more financial help.

"To tackle this devastating condition, we are also doubling funding for research, pushing the NHS to improve diagnosis rates and post-diagnostic support, and focusing national attention on dementia like never before."