The Government's ditched coronavirus app only picked up contacts with iPhones 4% of the time, the Mirror understands.
Health Secretary Matt Hancock is set to announce the NHSX app has been scrapped - with the test and trace team putting all their efforts into a system offered by Apple and Google.
It follows months of warning by experts that the Government's in-house system would not work.
The Mirror understands the app under testing on the Isle of Wight only detected Android phones 75% of the time - and iPhones just 4% of the time.
Conversely, testing of the system offered by phone manufacturers was accurate 99% of the time.
But it's thought the built-in framework struggled to detect how far away another phone was - a crucial element of the test and trace procedure.
Ministers were warned in May, when it was announced the Government would be pursuing its own system rather than Google and Apple's framework, that the phone manufacturers wouldn't let third party apps use the bluetooth connection while the phone is locked.
The built-in system works in the background - allowing a much greater rate of tracking contacts between devices.
It's understood the team behind the NHSX app had been testing the Apple/Google system alongside their own system - as a "plan B".
The Health Secretary originally promised the app, which has been under testing on the Isle of Wight, would be rolled out across the nation in ‘mid-May’.
The version under testing on the Isle of Wight has not been set up to tell anyone to self-isolate - instead warning them to pay careful attention to social distancing guidelines if they've been close to someone who has reported symptoms.
Mr Hancock told Brits it was their “duty” to download it in large numbers in order to combat the spread of Covid-19.
But as the deadline was missed, Mr Hancock and test and trace chief Dido Harding have said it the “cherry on the cake” - and not essential to the contact tracing push.
And yesterday, Health Minister Lord Bethel indicated the delivery of the app had slipped even further.
He told the Science and Technology Committee the pilot of the app on the Isle of Wight had been successful, but also showed that people prefer human contact to a technological one.
he said: "We're seeking to get something going for the winter, but it isn't the priority for us at the moment."
He added that the Government was not feeling great time pressure over the app, and it did not want to "poison the pool" by rushing something out that isn't "quite right".
