Smart phones are being used as "pocket doctors" to spot early signs of Parkinson's disease from subtle changes in voice and movement.

Now there is an experimental "app" for diagnosing the neurological condition that affects about 127,000 people in the UK.

The system involves sensing almost imperceptible effects on the voice, walking behaviour and manual dexterity that may provide an early indication of Parkinson's.

Scientists are testing the app in a large group of 2,500 people with diagnosed Parkinson's, symptoms or genes known to be linked to the disease, and healthy individuals.

An earlier analysis of thousands of voice recordings suggested that effects such as increased breathiness, drifting pitch, and altered vowel sounds can detect Parkinson's with 99% accuracy.

Similarly, checking a person's gait with a smartphone's accelerometer - the in-built motion sensor that tells the device what way up it is - identified people with Parkinson's in 98% of cases.

Smartphone information could also be used to assess symptom levels and progression in those being treated for the disease, say the scientists.

Mathematician Dr Max Little, from the University of Aston, who is leading the research, said: "Not only can you predict whether someone has Parkinson's disease or not, you can actually score their symptoms on clinical scales.

"This new kind of remote data analysis will help patients to monitor their conditions on a minute-by-minute basis from the comfort of their own homes.

"Of course, it is still important that they receive regular advice and treatment from medical professionals, who may also benefit from this new technology.

"Physicians may be able to use data collected by their patients' smartphones to prescribe medications .. This information may also help examine people thought susceptible to developing Parkinson's disease. The condition is hard to diagnose, with specialists having to take a detailed history of people's symptoms and analysing them for physical signs of the disease.

"Using smartphone data may help to make this process much easier."

In the study, conducted with the help of scientists at Oxford University, participants are being asked to use a smartphone with the Parkinsons app at home for a week.

The voice test is involves making an "aah" sound into the phone's microphone, while gait is assessed while walking a distance of 20 paces. Another three-minute test measures manual dexterity.

Unusually for research on Parkinson's, participants have been recruited from a wide range of ages, with some as young as 20.

Parkinson's disease is rarely diagnosed in people young than around 50. But by the time it is detected from obvious symptoms such as tremor and rigidity the brain has already suffered significant damage.

"This study allows us to see if this technology can actually detect the disease before someone is diagnosable using standard techniques," said Dr Little, who spoke about his research at the British Science Festival taking place at the University of Birmingham. "The signs are promising. We've been able to show that this technique is extremely accurate; the question is how accurate. Can it pick up symptoms that are subtle and occur before obvious tremors?"

He acknowledged that there may be ethical issues involved in using a smartphone app to diagnose a serious disease.

"There are ethical questions that have to be addressed," said Dr Little. "One of the problems is that if you give people an app to use how would they interpret the results, and what would they do if they have positive results and aren't able to get treatment?

"On the other hand if you just restrict it to a clinical environment that creates a bottleneck and a shortage of people who are able to be treated."

His team is also looking at the possibility of using smartphones to measure symptoms of Friedrich's ataxia, a rare childhood condition that causes muscle weakness and loss of speech.

Promising work by other scientists suggested that voice analysis could also be used detect mental deficits linked to Alzheimer's and anxiety, he said.

Claire Bale, research communications manager at the charity Parkinson's UK, said: "This research is a welcome step forward. Parkinson's is a very complex and fluctuating condition, so effectively managing it is a real challenge.

"Smartphones offer huge potential as they continuously capture information, and can monitor subtle changes - such as an increase or decrease in someone's tremor. Arming doctors and people with Parkinson's with this technology could revolutionise the way the condition is managed."