Chancellor Rishi Sunak is set to unveil a multi-billion pound package of support for self-employed workers, amid growing anger that they are being forced to keep working during the coronavirus crisis or rely on benefits.

After Boris Johnson told MPs he wanted to offer "parity of support" to the country's 5 million self-employed people, there are expectations that the chancellor may offer government cash to pay a proportion of wages to those unable to work

But it is thought the package being announced at a Downing Street press conference at 5pm may be less generous than the 80 per cent payment - up to a maximum of £2,500 a month - provided to employees who would otherwise be laid off.

It is thought the scheme could be subject to a lower cap of around £1,700 a month, with payments calibrated according to an assessment of revenues and profits over the past three years.

The Resolution Foundation has calculated a scheme delivering "parity" with employed workers could cost Mr Sunak £3.6bn over three months for each 1 million participants. The thinktank estimates around one-third of self-employed people are having to give up or significantly scale back work because of sickness, the need to care for children home from school and the requirements of the government's lockdown order.

Boris Johnson is coming under intense pressure to provide generous support for the self-employed and freelancers, after Jeremy Corbyn warned him that construction workers were continuing to take the train to sites despite knowing they are infected with coronavirus.

At the last prime minister’s questions before the House of Commons broke up early for Easter, Mr Corbyn told Mr Johnson that NHS workers were being put at risk because the self-employed could not afford to follow the official advice to stay home, because they have nothing but Universal Credit to fall back on if their income stops. The Labour leader called for building sites to be shut down immediately unless they were doing emergency work.

At a later press conference in 10 Downing Street, Mr Johnson confirmed that the chancellor’s package of support would be unveiled on Thursday.

He said the government had put together “an unprecedented programme of support not just for businesses but for workers of all kinds across the country”, adding: “We will do whatever we can to support the self-employed, just as we are putting our arms around every single employed person in this country.”

The announcement of support for the self-employed had been delayed because the complexity of their working arrangements, compared to staff members taxed through the PAYE system, made it harder to come up with “the right tailored programme”, the prime minister said.

Mr Sunak’s package comes after a string of NHS staff complained of being forced to travel in overcrowded London Underground trains to hospitals in the capital because so many non-emergency workers were continuing to commute into the city, putting them at risk of becoming infected with coronavirus.

The mayors of London and Manchester, and leaders of Scotland, Wales and Northern Ireland have all joined calls for a halt to non-essential building work.

London mayor Sadiq Khan said: “It remains the case that too many of the people using [Transport for London] services at the busiest times work in construction. The idea that construction workers can stay two metres apart during the course of a busy day, but also the idea we can’t put on hold certain construction work in light of this public health crisis, I find astonishing.”

But communities secretary Robert Jenrick insisted it was “sensible” for construction work to continue if “safe to do so” and if employers follow Public Health England’s social distancing guidance.

And the PM resisted calls to order builders to down tools, telling the Commons: “What we are not doing is closing down the whole UK economy.”

Making his final appearance at the despatch box as Labour leader, Mr Corbyn told MPs: “Construction sites are still operating on non-emergency work despite the new rules.

“We heard this morning on the radio a call from a self-employed construction worker who said he had contracted coronavirus, he was suffering from it and knew he had got it but had no other option but to get on the London Tube and go onto a site to work, obviously putting himself at greater risk and putting all other passengers and all other workers on that site at risk.

“Why was he doing it? Because the site had not been closed down and he had no other source of income to feed his family, so he’s going to work putting all of us more at risk as a result.”

Industry representatives are understood to have demanded further “clarity” from the government, raising concerns that current measures are risking the lives of employees and those they may come into contact with.

One site worker, an electrician in east London who gave his name as Nelson, told Radio 4’s Today he decided to stop working for fear he could be spreading Covid-19.

“People know of people who are now in hospital and they’ve caught it on site,” he said.

“There seems to be a lot of continued lack of distancing taking place and obviously the cross-contamination is rife. Personally, I need to be earning money, otherwise in a month I’m going to feel the pinch.”

Jeremy Corbyn said he would ‘not [disappear] from anywhere’ at Prime Minister's Questions on 25 March 2020 (Reuters TV)

Mr Corbyn called on the prime minister to give “unequivocal guidance” now that construction work on non-emergency jobs should stop immediately.

Mr Johnson responded: “Everybody should work at home unless they must go to work, unless they have no alternative and can’t do that work from home.”

But he added: “If a construction company is continuing, then clearly they should do so in accordance with the guidance of Public Health England and they have a duty of care to their employees.”

Speaking later, the prime minister insisted that the country would get through the coronavirus crisis.

“When you look at the sheer scale of what the government is doing to get this country through, we will cope – and we are coping – very well indeed under the most challenging possible circumstances,” he said.