Whatever happened to the NHS contact-tracing app?

The news that the full test-and-trace programme might not be up and running until September has led some to think this applies to the NHS contact-tracing app, rather than the wider manual tracing effort.

The confusion is understandable - after all it's not long ago that ministers talked as if the app was the centrepiece of the programme rather than the "cherry on top" as Baroness Harding described it this week.

My understanding is that the app, which has indeed suffered a number of delays, should still be rolled out nationwide by late June or early July - although there is no guarantee that the timetable won't slip further.

After a first trial with an app with very limited capabilities on the Isle of Wight, version two, which features five questions about symptoms instead of two and integrates the testing process, is undergoing testing at a secret location in London.

I understand this version will then be launched as an update for Isle of Wight residents next week.

But when that local trial becomes a national rollout is not clear.

Someone close to the project says that at the beginning, the team was told to act like a tech start-up, trying things out and then changing them day by day.

Now, that person says: "Downing Street's attitude to risk has been dialled right down - they don't want it to be released until it's perfect."

Bluetooth contact tracing apps are a new idea and many countries around the world are trying them out.

So far, however, there is no clear evidence that they are effective.

Singapore, which pioneered the idea, struggled to get enough people to download its app, which appeared not to work very well.

Now the government there says it will roll out a wearable contact-tracing device to all its citizens instead.