Ministers are looking at ending the coronavirus lockdown with a “gradual sector-by-sector approach” that could see vital industries such as manufacturing get back to work before less critical ones like entertainment, according to Whitehall sources.

Two officials said one of the main options being explored for ending the lockdown was the idea of a phased return by industry, with civil servants in the Department for Business, Energy and Industrial Strategy among those looking at how it could work.

With UK-wide deaths at almost 900 a day, Dominic Raab, the foreign secretary, confirmed on Thursday that measures to stem the spread of the disease would remain in place until there is evidence that the number of fatalities has reached its peak.

Raab – who is deputising for the prime minister while he remains in hospital with Covid-19 – told the daily Downing Street press conference that it was too early to lift the restrictions on people’s daily lives, without saying how long they would last for. “We are not done yet. We must keep going,” he said.

“It’s been almost three weeks and we’re starting to see the impact of the sacrifices we’ve all made. But the deaths are still rising and we haven’t yet reached the peak of the virus. So it’s still too early to lift the measures that we put in place. We must stick to the plan and we must continue to be guided by the science.”

Science Weekly Covid-19: how do you lift a lockdown? Sorry your browser does not support audio - but you can download here and listen https://audio.guim.co.uk/2020/04/08-57750-gnl.sci.20200409.ms.covid_19_lockdown.mp3 00:00:00 00:14:45

Downing Street has repeatedly refused to set out the options for how the UK could end the lockdown, but insisted that the government was doing “extensive work” on the various possibilities.

The prime minister’s official spokesman said: “Work is underway on an exit strategy but the public wants us to be focused on stopping the spread of the disease while building up the NHS and saving lives … Whitehall is working extensively on this but the peak is not reached and the government needs to focus in its public messaging on staying at home to save lives.”

Officials acknowledge it could be difficult to rank sectors according to their importance to the economy, how much social contact they involve and the strength of their protective measures to keep people apart.

But they said it was more possible than other ideas that have been floated in recent days, such as letting 20 to 30-year-olds go back to their normal lives before older people.

Other ideas that have been raised by government scientists include “alternating between periods of more and less strict social distancing measures” for most of the year or providing “immunity passports” to those who have had the disease, although that would only work with a functioning home antibody test.

The lockdown measures – which were announced on 23 March – were first scheduled to be reviewed after three weeks, on Easter Monday. The legislation drawn up to implement the lockdown must be reviewed at least once every 21 days, making 16 April the latest this can be done.

Raab chaired a Cobra emergency committee on Thursday afternoon to discuss the lockdown with leaders of the devolved nations and the mayor of London. He said on Thursday evening that the government did not expect to say more about the possible easing of physical distancing measures until the end of next week.

It is understood that tightening the lockdown is under greater consideration at this point, although Priti Patel, the home secretary, told TalkRadio on Thursday that the government was “absolutely not” considering any further physical distancing measures.

One official said some Tory ministers and advisers have been pushing for the lockdown to end sooner rather than later, but that the current thinking was that it would have to last for another six to eight weeks.

Boris Johnson’s hospital admission and spell in intensive care had undermined the case of those pushing for schools and workplaces to soon get back to normal, the source said.

Industry leaders were briefed at the end of last week on the government’s ideas about a possible sector-by-sector approach when the lockdown ends, with manufacturing, logistics and food supply companies likely to be at the front of the queue if they are not still open already.

One person familiar with the government’s thinking said that the chief medical officer, Chris Whitty, was concerned about the idea, fearing compliance with the rules would collapse once the public could see workers from some sectors returning to a more normal life.

The government’s scientific advisers remain particularly concerned about the risk of a second wave of infections if the rules are relaxed too soon, the source said – but Whitehall officials are conscious of the prime minister’s desire to see them loosened as soon as possible.

Johnson and his ministers have acknowledged that widespread testing will be part of the answer, but the scientific advisers have said the capacity to roll out mass testing for live cases across the population is unlikely.

Labour is pushing for the government to publish an exit strategy even though the end of the lockdown is likely to be some way off, as the public would need to have confidence in the approach and time to get used to the idea.

Nick Thomas-Symonds, the recently appointed shadow home secretary, said: “While we acknowledge the difficulty in putting precise times on the strategy, one of the key reasons publication is necessary is to enable frontline emergency services to plan effectively.

“This is especially important in areas such as policing, where clear plans will need to be in place to ensure a managed process. That is why I urge the home secretary to help get an exit strategy published, as it’s a vital part of securing public confidence in the government’s approach.”