England and Wales will finally get a coronavirus tracing app on September 24, after months of delay

• The UK government is launching a contact-tracing app in England and Wales on September 24.
• The app will work by getting people to scan QR codes as they enter a venue and, if they subsequently experience coronavirus symptoms, to report that in the app so others can be alerted.
• The UK's journey to release a contact tracing app, which was originally promised to come out in May, has been tortuous and the government initially blamed Apple for the delay.

England and Wales will get an official contact tracing app, months after it was originally promised.

A contact tracing app for England and Wales will be arriving on September 24, the government confirmed on Friday.

"We need to use every tool at our disposal to control the spread of the virus including cutting-edge technology. The launch of the app later this month across England and Wales is a defining moment and will aid our ability to contain the virus at a critical time," said Health Secretary Matt Hancock.

Users will be able to scan QR codes at venues to keep a record of where they have been. If they later report themselves as having symptoms, the app can then be used to notify the venue and anyone else there who might have been at risk of infection.

It's not clear from the government's announcement exactly what other users might be told about whether they have to self-isolate.

The UK government is urging businesses and venues to make sure they have official QR codes ready for people to use, and businesses already using their own QR codes are being encouraged to switch over.

England and Wales have lagged behind the other UK nations in launching an app. Scotland launched its own contact tracing app on Thursday, and Northern Ireland launched its StopCOVID NI app on July 31. All these apps work using Bluetooth to keep a log of which other phones you have been in proximity with. If someone else who has the app reports themself as positive for COVID-19, the app alerts you.

BBC journalist Rory Cellan-Jones tweeted a picture of what the app looks like. It appears users will be able to self-report symptoms to trigger alerts, rather than having to provide a positive COVID-19 test.

The UK started developing a contact-tracing app in March, and originally said an app would be ready to roll out in May. It soon ran into technical problems however over getting the app to work properly, particularly on iPhones.

Apple and Google in May released a specialized toolkit, called the exposure notification API, for health agencies to help them overcome some of the technical problems the UK encountered. Apple and Google's tech requires that governments decentralize user data, making the apps more private and the data more difficult to pool together and study.

Initially the UK rejected the Apple-Google tech on the grounds it wanted to be able to centralize data to better understand the spread of the virus. In June however it performed a U-turn, admitting the technical challenges had been too great without the tech giants' help.