(Adds comments from Health Secretary, ICO, NHSX CEO)
By Paul Sandle
LONDON, May 4 (Reuters) - Britain will start testing its own COVID-19 tracing app on the Isle of Wight from Tuesday, hoping that the technology in combination with more testing and tracking will help limit transmission of the coronavirus.
It has taken a different approach from other European countries by processing data centrally rather than solely on the devices themselves, where a higher level of privacy can be guaranteed.
Health Secretary Matt Hancock said on Monday, however, that data privacy and security were paramount in the app's development.
Everyone on the island off the south coast of England, which has a population of about 140,000, will be able to download the app from Thursday, while health service and council staff will have access from Tuesday.
Anyone who has symptoms of COVID-19 or a positive test, enters their details on the app to start the tracing process.
"By downloading the app, you're protecting your own health, you're protecting the health of your loved ones and the health of your community," Hancock told a news briefing on Monday.
"The pilot is important so we can help make sure the app works as well as it possibly can alongside the contact-tracing system."
Countries are rushing to develop apps which, along with a wider testing and tracking programme, are seen as key to easing the social distancing rules that have all but shut global economies.
Britain has opted for a centralised model, whereby a list of contacts made via bluetooth signals are stored on a users' device as anonymous tokens.
If the user says they have symptoms or have tested positive, the list of contacts can be submitted to the app, which analyses the data and notifies devices matching the tokens it deems at risk, for example because of the time the devices were in proximity.
Matthew Gould, Chief Executive Officer the National Health Service's technology group NHSX which developed the app, said they had "put privacy right at the heart of it".
"It doesn't know who you are. It doesn't know who you've been near. It doesn’t know where you are," he said.
Rival systems, including one proposed by Apple and Google, match the lists of tokens on the devices themselves, removing the risk of sending data to a centralised server, even if it is anonymised.
Britain's Information Commissioner Elizabeth Denham said on Monday that if she were to start with a blank sheet for an app, decentralised would be on it.
But she told a committee of lawmakers that did not mean a centralised system could not have the same kind of privacy and security protections.
Gould said centralised technology would be able to give more insights into the virus.
"If privacy was the only thing we were optimising for here, then it may well be that a decentralised approach should be the default choice," he said.
But privacy had to be balanced against public health, and a centralised approach gave the potential "to collect some very important data that gives serious insight into the virus that will help us".
These included data on which symptoms developed into COVID-19, which contacts were more risky, and the difference, for example, between a contact three days ago and one yesterday.
He added that Britain was talking to international partners and was also working "phenomenally closely" with Apple and Google.
Ideally more than half the population would download the app, he said, but even a level above 20% would give some important insights into how the virus was spreading. (Additional reporting by Kate Kelland and William James; editing by Stephen Addison)