Apple and Google are said to be in a "standoff" with the UK's health service over its plans to build an app that alerts users when they have been in contact with someone with coronavirus.

Apple and Google announced on Friday that they are working together on Bluetooth technology to help governments and health agencies reduce the spread of the COVID-19 virus around the world.

Apple says that user privacy and security will be central to the design of the project, which will use a decentralized API to prevent governments from building a surveillance-style centralized database of contacts.

However, according to The Guardian, that means if the NHS goes ahead with its original plans, its app would face severe limitations in its operation.

NHSX – the British health service's digital innovation unit – reportedly wasn't aware of Apple and Google's project before it was announced, and it now looks like the usefulness of its own app will be severely hampered or even rendered non-functional if it doesn't implement the protocol.

That's because without adhering to the Apple and Google API, a contact tracing app won't be able to access Bluetooth when it's running in the background, and would only work when the app was open and the phone unlocked.

Similar limitations have been demonstrated in Singapore's contact tracing app, TraceTogether, which requires the user to leave their phone unlocked to work properly. The app has a three-star rating on the App Store and has been installed by just 12 percent of the country's population.

For its part, a spokesperson for NHSX denied claims of a "standoff," telling The Guardian: "This suggestion is completely wrong. Everyone is in agreement that user privacy is paramount, and while our app is not dependent on the changes they are making, we believe they will be helpful and complementary."