Downing Street has moved to combat confusion over how people should respond if “pinged” as a contact by the NHS Covid-19 app.

Number 10 said it was “crucial” for people to quarantine in line with the app’s recommendation, just hours after a Government minister suggested people should make an “informed decision” about whether to obey the technology.

Business minister Paul Scully said self-isolating after being told to by the app was a decision for individuals and employers.

Another minister in the business department, Lord Grimstone of Boscobel, stressed in a letter to one large employer that the app was only an “advisory tool” and that people were not under any “legal duty”, The Times reported.

Although it has never been a legal requirement to obey the app’s instructions, the official NHS guidance has been that people should “self-isolate immediately” when told to.

Given the risk of having and spreading the virus when people have been in contact with someone with Covid, it is crucial people isolate when they are told to do so, either by NHS Test and Trace or by the NHS Covid app

In a sign that Downing Street was scrambling to get its message back on track, a No 10 spokeswoman said: “Isolation remains the most important action people can take to stop the spread of the virus.

“Given the risk of having and spreading the virus when people have been in contact with someone with Covid, it is crucial people isolate when they are told to do so, either by NHS Test and Trace or by the NHS Covid app.

“Businesses should be supporting employees to isolate, they should not be encouraging them to break isolation.”

Earlier, Mr Scully told Times Radio: “It’s important to understand the rules. You have to legally isolate if you are on the… contacted by Test and Trace, or if you’re trying to claim isolation payments.

“The app is there to give… to allow you to make informed decisions. And I think by backing out of mandating a lot of things, we’re encouraging people to really get the data in their own hands to be able to make decisions on what’s best for them, whether they’re employer or an employee.”

Asked whether this meant people should or should not self-isolate if “pinged”, he said: “We want to encourage people to still use the app to be able to do the right thing, because we estimate it saves around 8,000 lives.”

However, he added that it was “up to individuals and employers”.

On Monday night, Boris Johnson had stressed the importance of self-isolation as “one of the only shots we have got left in our locker to stop the chain reaction of the spread of Covid” following the lifting of England’s restrictions.

“I’m afraid that at this stage it’s simply a consequence of living with Covid and opening up when cases are high in the way that we are,” he said.

Asked about the chaotic handling of the issue, Home Office minister Chris Philp said: “I don’t think it is in a mess.”

He told Times Radio there had been a “consistent” approach that “if people are pinged by the app they should self-isolate”.

Professor Sir Jonathan Montgomery, who chaired the ethics advisory board for NHSX on its contact tracing app, told Times Radio the Government needed to give clearer guidance to people about what to do when told to self-isolate.

“When we had no protection the risk was the same for everybody. If that risk is now reduced because someone is double-vaccinated, it feels as though we need more sophisticated advice,” Sir Jonathan said.

“If we are visiting an elderly relative or a cancer patient then take the ping seriously, but if you are doing something relatively Covid-friendly, then maybe make a different decision.”

Professor John Edmunds, a member of the Scientific Advisory Group for Emergencies (Sage), which advises ministers, said: “Contact tracing and self-isolation play an important role in stopping cases getting out of control and preventing deaths.

“It’s important we maintain these measures as stringently as we can.”

Shadow health minister Justin Madders said: “The Government is making it up as they go along.

“Ministers mix messages, change approach and water down proposals when the public and businesses need clarity and certainty.”

Meanwhile, the Prime Minister is facing a backlash over his plans to make coronavirus vaccination compulsory for nightclubs and other crowded venues in the autumn.

Clubs, backbench Tories and opposition MPs criticised Mr Johnson’s announcement on Monday – the day that clubs in England were allowed to open for the first time since March last year.

Night Time Industries Association chief executive Michael Kill accused the Government of “an absolute shambles”.

Mr Scully, the minister for small business, said the policy would not be introduced until the detail is right.

He suggested that pubs would not be included, with the use of the vaccine passports aimed at nightclubs and “larger ticketed events”.

“There are a number of sporting venues that are already looking at voluntarily doing this,” he told Sky News.

Mr Scully admitted to having reservations about the plan: “I’m not comfortable that Government is mandating anything frankly, I’m a very libertarian Conservative, I want to be able to back off – that’s why yesterday was an opportunity for Government to back off from so many different things and let people live their lives.

“But what we have to do is make sure that people will also live their lives safely, the NHS can function safely, and these are the challenges that we still have to do.

“So it’s incredibly frustrating, it’s incredibly complicated to work through the detail, but that’s the challenge we have.”