Over half a million people were “pinged” by the NHS Covid-19 tracking app in England in the week to July 7, the highest figure since its launch.
Some 520,194 alerts were sent instructing users to isolate for up to 10 days because they had been in close contact with someone who tested positive for coronavirus.
Plans to make the app app less sensitive to reduce disruption caused by mass isolations have been pushed back as concern mounts about rising infection rates.
No change is expected to the app for several weeks and may not come until an overhaul of isolation rules on August 16 that will exempt the double vaccinated from having to quarantine.
The latest figure, taken from NHS data, has jumped 46 per cent from 356,677 the previous week and is the highest since the app launched at the end of September last year.
Wales, which uses the same app, also recorded the highest number of alerts since the tool launched, with 9,932 people pinged. Scotland and Northern Ireland have their own versions of a tracing app.
The app uses Bluetooth signals to determine how close someone is to another person and currently considers proximity of two metres or less for more than 15 minutes as an infection risk.
More than 26.5 million people have downloaded the app in England and Wales, with more than 342,000 more downloads in the past week alone, but ministers are concerned that many people are also deleting it from their phones because of the number of times they have been alerted.
There are no official figures for deletions as use of the app is voluntary. However, the number of people checking in at venues with the app has steadily dropped since the start of June, with 11.3 million check-ins made in the week to July 7, compared with 14 million in the first week of June.
Some companies are reportedly missing 20 per cent of their workers.
Production at Nissan’s Sunderland car plant has been hit by a reported 700 workers being alerted and advised to isolate by the app, equating to about 10 per cent of the workforce.
Earlier this week, large queues built up at Heathrow after more than 100 staff members at the airport were told to self-isolate by the app.
Staff at restaurants and pubs have also been badly affected by being “pinged”, with Kate Nicholls, chief executive of UK Hospitality, saying that in some cases up to one third of staff have been forced to stay at home.
Robert Jenrick, the communities secretary, said he was concerned about the number of people taking time off work after being told to self-isolate by the app.
He told LBC Radio: “It is important that we have the app, that we take it seriously, that when we do get those messages we act accordingly”, but added that ministers were giving “further thought” on how the government can ensure it is a “proportionate response.”
Commenting on the news, Lord Bilimoria, CBI President, said: “It’s a genuine shock that more than half a million people in the UK were asked to self-isolate in just one week alone.
“Infection rates may be increasing rapidly but it’s clear the test and trace system needs an overhaul, with over 2/3 of the adult population now fully jabbed.
“As more businesses prepare to open their doors on Monday staff shortages are being felt acutely across all sectors and in all areas of business particularly, hospitality and leisure.
“The Government should urgently bring forward its plans to 19 July – currently set for 16 August – to allow double-jabbed individuals not to self-isolate if they have been informed by NHS Test and Trace that they have come into contact with a Covid positive individual.”