Media playback is unsupported on your device Media caption Tom Coppins speaks of the frustration and fear he has regarding his dementia

Leading nations have committed to developing a cure or treatment for dementia by 2025 at the G8 dementia summit.

Health ministers meeting in London said it was a "big ambition" and that they would significantly increase funding for research to meet that goal.

The UK has already said it aims to double its annual research funding to £132m by 2025.

The global number of dementia sufferers is expected to treble to 135m by 2050.

The G8 said it would "develop a co-ordinated international research action plan" to target the gaps in research and ways to address them.

Dementia across the globe 44 million globally have dementia

135 million will have the disease in 2050

By then 71% will be poor and middle income

$600bn global cost of dementia

In the UK, cancer research gets 8x as much funding as dementia Source: Alzheimer's Society

It also called on the World Health Organization to identify dementia as "an increasing threat to global health" and to help countries adapt to the dementia timebomb.

In a statement it said "We recognise the need to strengthen efforts to stimulate and harness innovation and to catalyse investment at the global level."

Dementia is incurable and ultimately leaves people needing full-time care as brain function wastes away.

There is growing concern that some countries will simply not cope with the growing burden of dementia.

It costs the world billions of dollars each year: £370bn ($604bn) in 2010, according to the World Health Organization.

Health ministers from the G8 nations are meeting - under the presidency of the UK - to find the best ways to advance research.

Analysis Dementia is heading towards being the biggest health and care problem of a generation so you'd think it would have the funding to match. Yet it really is the poor relation of other diseases. In the UK, about £590m is spent on cancer research with £267m coming from government. At the moment £52m of government money goes to dementia research. It's a pattern reflected around the world. Part of the problem is that until recently dementia was considered a "normal part of ageing" whereas cancer has been documented as far back as ancient Egypt. It means dementia research is starting from a low base. The UK is aiming to double its spend, but this will still leave dementia significantly behind. The Alzheimer's Society says it expects more. Dealing with dementia: Your stories

David Cameron called on governments, industry and charities all to commit more funding. He said the G8 should make this the day "the global fight-back really started".

He said the UK Government would boost annual research funding from £66m, the 2015 pledge, to £132m, which will be adjusted for inflation, by 2025.

Mr Cameron told the summit: "This disease steals lives, wrecks families and breaks hearts."

"If we are to beat dementia, we must also work globally, with nations, business and scientists from all over the world working together as we did with cancer, and with HIV and Aids.

"This is going to be a bigger and bigger issue, the key is to keep pushing."

The health secretary Jeremy Hunt said: "The amount [of money] going into research is too little.

"We would like a cure to be available by 2025. It's a big, big ambition to have. If we don't aim for the stars we won't land on the moon."

However, so far only the UK has made a definite funding announcement with the other nations committing to "a significant increase in overall dementia research".

Mr Hunt said a Dementia Envoy would be appointed that would also help industry and charities boost funding.

'Global leadership'

The chief executive of the Alzheimer's Society, Jeremy Hughes, said: "Today the UK has demonstrated global leadership on tackling dementia.

Video stories A close look at dementia's human cost

"Dementia has come out of the shadows and is centre stage - but we must ensure G8 has a lasting legacy.

"The governments' have all committed to updating progress on research biannually, but every month counts for the millions of people living with dementia worldwide."

Hilary Evans, from the charity Alzheimer's Research UK, said: "This action plan is the best possible news for people living with dementia, it tells them that the world will fight for them, and that the best and most collaborative science is our greatest weapon.

"With the right investment, we can be more optimistic than ever that we will meet if not exceed the G8's 2025 target."

Bran scans

A dementia brain scan will also be introduced for some NHS patients with complicated symptoms.

It could help rule out Alzheimer's disease, the most common form of dementia, by hunting for damaged proteins in the brain.

A radioactive marker which binds to amyloid, a hallmark of Alzheimer's disease, will be injected. If there is amyloid in the brain then the tracer will show up on brain scans.

The test will initially be offered at Imperial College Healthcare NHS Trust in London and will be rolled out to other specialist centres.

What is dementia? It is an umbrella term that describes about 100 diseases in which brain cells die on a huge scale

All damage memory, language, mental agility, understanding and judgement

Alzheimer's disease is the most common form, affecting 62% of those living with dementia

It gets worse with time and eventually people are left completely dependent on carers

It is incurable World dementia cases 'set to treble' The dementia timebomb

Dr Richard Perry, a consultant neurologist at Imperial, told the BBC: "For a patient who can't get an answer using the usual tests this will make a big difference as it'll provide clarity.

"Knowing the cause is the first step to getting treatment."

Around 100 patients a year are expected to get access to the scan.

Media playback is unsupported on your device Media caption David Cameron: ""If we are to beat dementia, we must also work globally"

There have been a flurry of other funding announcements tied to the talks including:

The Medical Research Council (MRC) will commit £50m to improve treatments and delay the progression of the disease

The Alzheimer's Society has promised to spend at least £100m on research in the next decade

A new £3m "Dementia Consortium" will unite the charity Alzheimer's Research UK, two pharmaceutical companies and MRC Technology in the hunt for new drugs

The Engineering and Physical Sciences Research Council has put up £5m improve ways of diagnosing and measure disease progression.

Meanwhile, the Care Quality Commission (CQC) plans unannounced inspections of the care of dementia patients at 150 institutions across England.

The CQC said it would look at what needed improving, how to cut hospital admissions from care homes and ways to help people with dementia maintain their physical and mental well-being.

David Behan, chief executive of the health regulator, said: "We know that these people are often vulnerable because of their condition and can rely on a number of services across health and social care to support their physical, mental and social well-being.

"Our findings will draw conclusions on a national scale about what works well and where improvements are required."

A national report on the issue will also be published in May.