Downing Street has insisted it is "crucial" to slotxo online self-isolate when sent an alert by the Covid app - and businesses should help employees to do so.
It comes after business minister Paul Scully said he would encourage people who are "pinged" to self-isolate but they can make an "informed decision".
The app has always been voluntary to download and any alerts are advisory.
Labour accused the government of "making it up as they go along" and creating confusion.
In recent days, there has been widespread criticism that the app has been sending out so many alerts that hundreds of thousands of people are self-isolating and missing work, causing widespread disruption.
Pub chains, supermarkets, transport networks and other businesses have warned of the crippling effect blanket stay-at-home orders for close contacts were having on their operations.
People who are "pinged" by the NHS Covid app and told they have been in close contact with someone with coronavirus are advised - but not legally obliged - to self-isolate for 10 days.
However, anyone contacted directly by NHS Test and Trace - either by phone, text or email - must self-isolate.
On Tuesday, the UK reported a further 46,558 new daily Covid cases alongside another 96 deaths within 28 days of a positive test.