Health minister Ed Argar has said the Government is “doing the responsible and sensible thing” by asking the public sector to prepare for a worst-case scenario of up to a quarter of staff off work.

It comes as the UK Health Security Agency (UKHSA) warned that cutting the Covid-19 isolation period to five days would be “counterproductive”, and could actually exacerbate staffing shortages.

As it stands, people who receive negative lateral flow results on day six and day seven of their self-isolation period, with tests taken 24 hours apart, no longer have to stay indoors for a full 10 days.

There have been calls to further slash this period to five days.

But the UKHSA said in a blog published on Saturday that shortening the time spent in isolation beyond the current seven-day minimum would be “counterproductive”.

“In some settings, such as hospitals, it could actually worsen staff shortages if it led to more people being infected,” it said.

This comes as public sector leaders have been asked to prepare for a worst-case scenario of up to a quarter of staff off work as coronavirus continues to sweep across the country.

The Cabinet Office said on Saturday that, so far, disruption caused by Omicron had been controlled in “most parts of the public sector”.

But it said leaders had been asked to test plans against 10%, 20% and 25% workforce absence rates.

Mr Argar said this was a “responsible” move from the Government.

Our current assessment is that shortening the isolation period further beyond the current seven days... would be counterproductive

Asked on Times Radio about the advice, he said: “What you’re talking about there is Government doing the responsible and sensible thing of preparing for a range of contingencies, making sure that it considers all possible eventualities, even those that are at the very high end of the scale.”

On whether he thought such absence levels were likely to eventuate, Mr Argar said: “I think we model a range of scenarios up to things we think are highly unlikely, but you still do it because that’s what a responsible Government does in preparing for all eventualities.”

In its blog, the UKHSA said: “Our current assessment is that shortening the isolation period further beyond the current seven days (including the end of isolation assurance-testing) would be counterproductive. In some settings, such as hospitals, it could actually worsen staff shortages if it led to more people being infected.

“We will of course keep this position under review as evidence accumulates and as the Government monitors workforce impacts of the isolation policy in critical sectors.

“In particular, our assessment may change as we continue to learn more about the features of the Omicron variant compared to, for example, the Delta variant.”

Pressed on the prospect of cutting the isolation period to five days, Mr Argar said the Government had not yet received scientific advice to that effect.

He told Times Radio: “The clinical advice or scientific advice we have is around (moving) it from 10, as we have done, to seven days. We haven’t received scientific advice that it should go lower than that, and we will follow the scientific advice.

“I can entirely understand trusts and others wanting to use whatever levers they have to try to manage and reduce those staff absences but in something like this around the self-isolation period… it’s right that we follow scientific advice and we haven’t had scientific advice to cut that at this point.”

Chris Hopson, the chief executive of NHS Providers which represents health trusts, previously said that a decision to cut the period from seven to five days was a “risk judgment” the Government would need to take.

In a Twitter thread on Thursday, Mr Hopson said staff absences due to Covid-19 were “clearly now having a significant impact” across the whole economy and parts of the health service.

He added: “If staff absence rates and care quality/patient safety (sic) risk rise, pressure for a change to the isolation period will, inevitably, rise as well.”

Sir Frank Atherton, the chief medical officer for Wales, suggested “anybody who has a cold” should stay at home to curb the spread of the virus.

He told Times Radio: “I would say anybody who has a cold, or symptoms of a cold – a runny nose, a cough, sneezing, is it really appropriate for you to go on a train or a plane or a bus? You know, stay home, get better.”

Meanwhile, shadow health secretary Wes Streeting said the Government must “get its act together” on Covid testing supply.

He told Sky News: “The Government does need to get its act together on the supply of testing.

“And I think the Health Secretary needs to explain why it was that only three weeks ago he told me in the House of Commons that availability of tests wasn’t a problem.

“And yet now it so clearly is.”

Key workers including police and civil servants have said they do not believe they will be heavily affected by coronavirus staff shortages, while train operators have been running reduced timetables.

A National Police Chiefs’ Council spokesman said: “We continue to closely monitor absence rates within policing, which are not currently impacting on our ability to provide our normal service to the public.

“Forces have appropriate plans in place to manage the impact of the Omicron variant with good stocks of tests and PPE.

“Best use of PPE guidance has been vital in ensuring the absence rate stays within manageable levels, protecting officers when they’re out and about in public.”

Dave Penman, the general secretary of the FDA trade union which represents professionals and managers in public service, said: “The lessons learned from the first lockdown of the pandemic have helped the civil service to develop a flexible working model that, it many cases, enables it to work seamlessly between home and office.

“This innovation, together with continued investment to support flexible working, will help off-set some of the impact of those who have to isolate but are still well enough to work.

“No public service can continue to operate at the same level with a 25% reduction in staffing. However, the flexibility that’s been hard-wired into working practices will help offset some of the impact, something to be celebrated, rather than continually criticised by ministers.”

In recent weeks rail firms across Britain have axed trains at short notice due to staff self-isolating or feeling unwell, but industry leaders have said they have no plans to bring back former or retired staff.