Tens of thousands of taxi drivers, cleaners and shop workers are to be tested for coronavirus amid concern that they are spreading the disease.
Addison Lee, BT and Boots are among some of the firms whose staff will be given tests even though they appear healthy.
The Department of Health and Social Care has said it will help scientists understand the prevalence of the virus in asymptomatic people in higher-risk jobs. Scientists are divided over the extent to which asymptomatic carriers of Covid-19 are infectious.
Each of the partner businesses will have access to 10,000 tests, either in the form of home-delivery kits or through a mobile testing unit.
The announcement could pave the way for routine systematic testing of staff in high-risk occupations, something the former Health Secretary Jeremy Hunt and others have been calling for in recent weeks.
The study will also target geographical areas thought to be high risk, working with local authorities in Bradford and Oldham and the London boroughs of Brent and Newham. Tests in these areas will be carried out at walk-in test sites.
The announcement comes as the weekly statistics for the flagship Test and Trace service revealed that the proportion of close contacts of people who have tested positive for the disease fell again.
In the week ending July 1, 70.8 per cent were successfully reached and advised to self-isolate, compared to 74.2 per cent the previous week. Officials say this is because, with the easing of lockdown, people who test positive are tending to provide higher numbers of close contacts.
The figures show that the turnaround time for tests is improving, but confirmed that Boris Johnson's target for all in-person tests to be turned around within 24 hours by the end of June had been missed.
Overall, 31,421 people who tested positive for Covid-19 in England had their case transferred to the NHS Test and Trace contact tracing system during the first five weeks of its operation, the figures also showed.
Of this total, 23,796 people (76 per cent) were reached and asked to provide details of recent contacts, while 6,645 people (21 per cent) were not reached. A further 980 people (three per cent) could not be reached because their communication details had not been provided.
The figures cover the period May 28 to July 1. During that time, 144,501 people who had been identified as recent close contacts of people who had tested positive were reached and asked to self-isolate. This was 85 per cent out of a total of 169,863 identified close contacts.
The number of people identified as close contacts fell in the last week of the data, with officials saying this was due to fewer contacts being in care homes. The percentage of contacts reached has gone down from 74.2 per cent in the week ending June 24 to 70.8 per cent in the week ending July 1.
When combining the figures for all methods of community testing – home-test kits, regional test sites, mobile testing units and "satellite" test centres – a total of 54.9 per cent of people received their results within 24 hours in the week ending July 1, up from 41.3 per cent in the previous week.
Some 34.9 per cent of people waited between 24 and 48 hours (down from 44.6 per cent), 7.5 per cent waited between 48 and 72 hours (down from 10.6 per cent) and 1.8 per cent waited longer than 72 hours (down from 2.5 per cent).
Baroness Dido Harding, the executive chair of NHS Test and Trace, said: "We are committed to continually improving NHS Test and Trace, to reach more people at risk of passing the virus on as quickly as possible.
"This week we have seen test turnaround times improve further, with the majority of positive cases reached by contact tracers in under 24 hours.
"Anyone with symptoms can easily book a test, expect rapid results, and will hear promptly from NHS Test and Trace if they are tested positive.
"I continue to applaud all those who have played their part, got a test after experiencing symptoms, and responded to the service. I urge anyone contacted by NHS Test and Trace to follow the advice they receive to protect their families and communities."