The Government has been urged to take the “difficult decision” and ban non-essential construction work.
Mayor of London Sadiq Khan’s office said the Government must act urgently to get more people staying at home following construction workers reporting to building sites and images of packed Tube trains appearing on social media.
The response comes after Health Secretary Matt Hancock said that the Tube should be running in full so that people are spaced out and can be further apart.
However, a Scottish construction worker, who asked to remain anonymous, told the PA news agency: “We feel like our lives don’t matter, and our families lives don’t matter.
“We have been told if we don’t go into work tomorrow we will only receive statutory sick pay, and that’s not enough, so we feel like we are being forced into work. We don’t feel safe.”
Mr Hancock also said construction workers could continue to go to work as long as they could remain two metres apart at all times.
But a spokeswoman for the mayor said the Government needed to provide “proper financial support” to freelancers and the self-employed.
She added: “The Government must act urgently to get more people staying at home rather than going to work unnecessarily – that means taking the difficult decisions they are refusing to take to ban non-essential construction work and provide proper financial support to freelancers, the self-employed and those on zero-hours contracts to stay at home.”
The union Unite said construction workers were facing the choice of risking their health or losing their job.
Assistant general secretary Gail Cartmail added: “There is an immediate public health emergency on construction sites, due to a lack of social distancing.
“By construction workers being compelled to work unprotected and travel, the lack of Government safety coordination, is risking their health, the health of their families and the health of the general public.”
One worker who spoke to PA said large companies were deliberately ignoring advice from First Minister Nicola Sturgeon to cease all “non-essential” construction work.
He said the site where he works, Queen Street Station in Glasgow, is the busiest train station in Scotland, but that the work was not essential.
“The advice being given by ScotRail is to “stay home and save lives”, but that does not apply to us,” he said.
“Sturgeon can talk all she wants but until she puts into practice what she’s seen and actually make demands of these companies, we are lost in limbo between Johnson, his subordinates and then our own devolved parliament.”
After more scenes of packed Tube trains on Tuesday morning, Mr Khan told ITV’s Good Morning Britain he had told Mr Johnson “forcibly” at a Cobra meeting that construction workers should not be going into work.
But Downing Street has defended its position and said that construction work should continue despite the country going into lockdown if it can be done following Public Health England and industry guidance.
The Prime Minister’s official spokesman said that the Construction Leadership Council had issued guidance to the industry.
He added: “We urge employers to use their common sense when managing live projects and ensuring that employees can follow the Government guidance and practice safe social distancing on site.”
Scotland’s First Minister Nicola Sturgeon said it was clear construction sites should “be closed unless the building that is being worked on is essential, such as a hospital”.
A crane operator at a London construction site with 400 to 500 workers said: “Everyone on site at the minute feels angry and unprotected.”
The man, who asked not to be named, said if he opted not to go in he “wouldn’t get paid or even could lose my job”.
He added: “(It’s) scary really – I’ve got a family and kids at home. I’m in London around all these people, bringing it all back into an isolated home.”
Electrician Dan Dobson said the Government must provide support to self-employed workers, including about a million in the construction industry, and then shut down building sites.
He added: “Everyone on site at the minute feels angry and unprotected.
“None of them want to go to work, everyone is worried about taking it (coronavirus) home to their families.
“But they still have bills to pay, they still have rent to pay, they still have to buy food.
“Construction sites will stay open until the Government issues an order to close.
“But the Government cannot issue the order to close until it offers support to the one million-plus construction workers – it has to go hand in hand.”
While some companies said they were closing sites down and suspending work, others said they would remain open with “strict precautions” in place.
Transport for London (TfL) announced on Tuesday that work on its Crossrail sites was being temporarily suspended, but that essential maintenance of the transport network will continue.
HS2 said it will be reviewing the majority of works on its construction sites in line with the Government’s advice on dealing with Covid-19.
House-builder Taylor Wimpey also said it has closed its construction sites, show homes and sale sites.
But earlier on Tuesday, rival Redrow said its sites remain open with “strict precautions in place including enhanced levels of cleaning, additional hygiene facilities and social distancing”.
A Department for Transport spokeswoman said: “Our roads remain open and we expect works, including emergency and other street works to maintain utility services to continue, ensuring that life-saving medicine, equipment, supplies and healthcare staff can travel across the country to where they are needed most.”