Spoke to a neighbour of my MIL’s last night, who is in his 70s. He has been ill with a non Covid related illness and had been self isolating. He had a consultant appointment at a local hospital and that was the only time he’d left home for ten days. He was taken by private car by his wife. Shortly after his return home, he was “pinged” by the NHS app. He went back into isolation, at home, in bed again, mainly due to his existing illness. At midnight, on the last day of the Covid isolation, his phone “pinged” again, saying that he had been exposed again to someone with Covid. The only person he had seen was his wife and she was definitely Covid free.
Turns out a family living across the road have had someone there with Covid symptoms. The only explanation is that their phone has somehow connected across the road.