Coronavirus testing rules are set to be eased to reduce the time people have to spend in isolation as Boris Johnson acts to combat staff absences in key parts of the economy and health service.

People who test positive on a lateral flow test will no longer need a confirmatory PCR to begin the self-isolation period if they do not have symptoms, potentially allowing them to return to work earlier, under plans being considered by ministers.

The change could be announced on Wednesday as the Prime Minister argues to his Cabinet they should stick by the Plan B measures in England despite admitting parts of the health service will feel “temporarily overwhelmed”.

He will also face Prime Minister’s Questions and then make a Commons statement where he will face possible challenges from Tory MPs critical of restrictions amid concerns over staffing shortages.

Under the changes to the testing regime, first reported by the Daily Telegraph, the PCR capacity in laboratories will be limited to those with Covid-19 symptoms.

Currently those without symptoms who test positive on a lateral flow are asked to order a PCR test and only begin their isolation period when they receive the second result, effectively forcing them to isolate for longer than seven days – particularly if there are delays in obtaining the confirmatory result.

Health minister Gillian Keegan told the BBC there was no “official news or updates” on the change but as lateral flow tests are accurate the Government was “looking at what makes sense, we don’t need to do things that are unnecessary”.

A Government source said the change was being discussed but details were “still being finalised”.

Ministers are also expected to approve the scrapping of pre-departure tests for travellers heading to England, with Transport Secretary Grant Shapps keen to help protect the beleaguered aviation industry.

The Omicron-driven surge in coronavirus cases and the knock-on effect of staff absences is already causing major problems in parts of the health service.

A string of NHS trusts declared critical incidents and hospitals in Greater Manchester said they will pause some “non-urgent” surgery over the “rising impact” of Covid-19 and staffing shortages.

A record 218,724 lab-confirmed Covid-19 cases were announced in England and Scotland on Tuesday, though the figure will have been inflated by delayed reporting over the holiday period.

Labour leader Sir Keir Starmer tested positive on Wednesday, meaning his place at Prime Minister’s Questions will be taken by deputy leader Angela Rayner.

NHS England figures showed 15,044 patients with Covid-19 were in hospital on Tuesday morning, with 797 requiring mechanical ventilation.

Ms Keegan acknowledged the pressure on hospitals, saying: “Right now, they are under extreme pressure with the Omicron variant, with the number of positive cases and the increase in hospitalisations, and at this point in time when they always have extreme pressure.”

Ahead of Wednesday’s Cabinet meeting, Mr Johnson confirmed he would stick with the Plan B measures including work-from-home guidance, mask-wearing and Covid health passes ahead of the scheduled review of the regulations due to expire on January 26.

At a Downing Street press conference on Tuesday, he argued the booster roll-out has given substantial protection and added: “So together with the Plan B measures that we introduced before Christmas we have a chance to ride out this Omicron wave without shutting down our country once again.”

Mr Johnson accepted the weeks ahead are going to be “challenging” and said “some services will be disrupted by staff absences” as he pledged to “fortify” the NHS to withstand the pressures and protect supply chains.

Under the measures, he said 100,000 “critical workers” including those in transport, policing and food distribution will get lateral flow tests on every working day starting on Monday.

But he accepted the NHS was moving to a “war footing” and acknowledged the health service is under “huge pressure” while hospital admissions are “high”.

Mr Johnson’s administration in Westminster has stuck with the Plan B restrictions for England, announced four weeks ago, despite tougher measures in other UK nations.

First Minister Nicola Sturgeon will update the Scottish Parliament on the pandemic in the afternoon.

Dr Mike Tildesley, from the University of Warwick and a member of the Scientific Pandemic Influenza Modelling group (Spi-M), told BBC Breakfast that “the impact of any interventions being introduced now would be that much less effective” than if they had been put in place earlier.

He would not agree to saying it was too late for restrictions, adding it was unclear the epidemic had peaked.

“The next few days will be really, really key for us to try to identify that – children are going back to school, we’ve had sort of differences in mixing patterns over the Christmas period and we are yet to see what happens in the data as a result of that,” he said.

“The next week or two we’ll have a real indication as to whether we really have peaked and things are starting to turn around, then we’ll have much more information as to what the effectiveness of interventions may or may not have been at this point.”