Funding for research into dementia is to be more than doubled by 2015 in a bid to make Britain a world leader in the field, David Cameron will announce.
The prime minister will declare on Monday that tackling the "national crisis" posed by the disease is one of his personal priorities.
He will say it is a "scandal" that the UK has not done more to address dementia, which is thought to affect 670,000 people although about 400,000 have not been diagnosed and do not know they have it. The cost to UK society is estimated at £23 billion.
Over the next 10 years, the number with the disease is expected to rise to one million.
Launching a "national challenge on dementia", Mr Cameron will set out plans to step up research into cures and treatments and to ensure that the health and social care systems are equipped to deal with the problem.
Overall funding for dementia research is to reach £66m by 2015, from £26.6 in 2010.
"One of the greatest challenges of our time is what I'd call the quiet crisis, one that steals lives and tears at the hearts of families, but that relative to its impact is hardly acknowledged," he will say.
"Dementia is simply a terrible disease. And it is a scandal that we as a country haven't kept pace with it. The level of diagnosis, understanding and awareness of dementia is shockingly low. It is as though we've been in collective denial."
The prime minister will say that the costs associated with the disease are already higher than those for cancer, heart disease or stroke.
"So my argument today is that we've got to treat this like the national crisis it is. We need an all-out fight-back against this disease; one that cuts across society.
"We did it with cancer in the 70s, with HIV in the 80s and 90s. We fought the stigma, stepped up to the challenge and made massive in-roads into fighting these killers.
"Now we've got to do the same with dementia. This is a personal priority of mine, and it's got an ambition to match.
"That ambition: nothing less than for Britain to be a world leader in dementia research and care."
Care services minister Paul Burstow said hospitals would be given an extra £54m to assist the diagnosis of dementia.
He told BBC Breakfast: "We know that if we diagnose it earlier in hospitals people will get treated better.
"They get the dignity they deserve and they often don't need to stay in hospitals long. That saves money but it also delivers good care for them."
Shirley Cramer, acting chief executive of Alzheimer's Research UK, said Mr Cameron's announcement was an "important step" in recognising and solving the challenge presented by dementia.
"David Cameron's announcements are a turning point in our battle to defeat dementia," he said.
"Of course, investment must continue to increase if we are to avert the drastic economic costs of dementia that lie in wait. Alzheimer's Research UK looks forward to working with Government to ensure that this new funding achieves what is so desperately needed - new treatments and therapies."
Jeremy Hughes, chief executive of Alzheimer's Society, said: "Today's announcement by the Prime Minister marks an unprecedented step towards making the UK a world leader in dementia.
"Doubling funding for research, tackling diagnosis and calling for a radical shift in the way we talk, think and act on dementia will help to transform lives.
"There are currently 800,000 people with dementia yet too many are not able to live well with the condition. The PM is leading the way, but from Plymouth to Preston, from the boardroom to bus drivers, we all have a role to play."
Sir Mark Walport, director of the Wellcome Trust, said: "Rising to this challenge will require excellence in medical research, so we can better understand the biology of dementia and use that insight to improve diagnosis and treatment.
"The dementia challenge, however, will not be resolved by the natural sciences alone. It will also require progress in social care, so that patients can be helped to live at home for longer, and so that relatives who care for their loved ones receive the support they need. And it will require action to raise awareness of this devastating condition, so that it is understood and not stigmatised."
But town hall leaders warned there was a "very real crisis" in the provision of care for the elderly and vulnerable.
David Rogers, chair of the Local Government Association's community wellbeing board, said: "Without fundamental reform and sufficient funding we risk losing the public's trust and confidence in our ability to do the best for people in later life.
"We now need politicians to transcend political point-scoring and wake up to the ticking demographic time bomb this country is facing.
"There needs to be urgent action to ensure the way we offer support to older people is fairer, simpler and fit for purpose in order to truly meet the needs of the most vulnerable members of our society."
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