Over-70s will soon be told to self-isolate for several months to shield them from coronavirus, the health secretary has confirmed.

Speaking on Sunday morning, Matt Hancock said the government would unveil a “cross-party” package of emergency powers on Tuesday and that the measure would be included.

But he declined to give more details about when or how the quarantine procedures for older people would come into force.

“That is in the action plan yes,” he told Sky News. “And we’ll be setting it out with more detail when it’s the right time to do so.”

The measure to isolate over-70s was first reported overnight after government sources briefed its existence to select journalists – an approach to transparency which has attracted criticism.

Labour’s shadow health secretary Jonathan Ashworth said: “It is utterly unacceptable for government sources to be briefing journalists overnight on issues which are fundamental to how we deal with this virus, very fundamental to how our society is going to operate in the coming weeks.

“If things have changed since Thursday, and they’re changing very quickly, then really the prime minister should be doing another press conference today.”

Speaking later on the BBC about the self-isolation measures for over-70s, Mr Hancock said: “We do not want formally to say yet that people should do that. The reason for that is simply this length of time that they’d need to stay self-isolated, stay at home to protect themselves – it’s a very big ask, it’s a very long time. We do know that if you ask people to do this sort of thing they can tire of it; we know it has negative impacts.”

He also confirmed that the police would be given emergency powers to arrest those not self-isolating, adding: “We are going to take the powers to make sure that we can quarantine people if they are a risk to public health, yes, and that’s important. I doubt that actually we will need to use it much because people have been very responsible.”

The government has come under pressure to justify why its so far lighter-touch approach differs from that adopted by most other comparable countries, and why the scientific advice it says it is following differs from that issued by the World Health Organisation and European Centre for Disease Control and Prevention.

Mr Hancock said that “each country is taking measures according to their own circumstances” and confirmed that the government would publish its scientific advice later in the week, as demanded by opposition parties.

He also said pursuing “herd immunity” was not part of the government’s strategy, contradicting previous reports and statements attributed to government sources.

One discrepancy between the government’s approach and international scientific advice is on testing. The government says testing and so-called “contact tracing” of who infected people have met is not necessary in many cases, but the World Health Organisation has said it should continue as a priority.

Our starting position unfortunately has been far worse than many of our other European nations British Medical Association council chair Dr Chaand Nagpaul

“I think we need to understand better why we should be taking a slightly different approach to some of our comparative countries and nations internationally,” Labour’s Mr Ashworth said.

He called on the government to be clearer, adding: “Certainty is everything, people need advice. This virus spreads quickly and it exploits ambivalence. We don’t want any ambiguity. People just want clarity, not briefings to journalists overnight – the prime minister should be out there daily speaking to the nation and explaining why things are changing.

“I appreciate this is fast-moving but what we’ve seen with the panic buying is a reflection of the uncertainty that is out there, which is why I would really urge the prime minister to be on the front foot ... people want that certainty and they want to be reassured that government has a grip.”

The health secretary also announced a national effort to produce and procure more ventilators for the NHS – after he accepted there would likely not be enough for the number of patients to come.

“We have around 5,000 ventilators, we think we need many times more than that,” he said. “We’re saying that if you produce a ventilator then we will buy it. No number is too high. We’ve been working with companies for some time but also to switch over production.”

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Asked whether there would be enough, he said: “You’ve heard me say that we don’t make guarantees in healthcare. This virus is clearly a huge challenge and we’re learning every day. I don’t make guarantees like that.”

But Mr Hancock also urged people to stop panic-buying food, emphasising that the government was “confident” there would be enough for everyone.

The chair of the British Medical Association’s council Dr Chaand Nagpaul said: “Our starting position unfortunately has been far worse than many of our other European nations.