Britain has given the green light for companies to start putting spades in the ground to build a new high speed rail line, saying work could proceed in line with coronavirus safety guidelines despite the national lockdown.

The prime minister, Boris Johnson, announced in February that the line, known as HS2, which connects London to northern England, would go ahead.

The government on Wednesday issued formal notification to the companies tasked with construction, allowing them to start work and providing them and their suppliers with business at a time when the pandemic has caused the UK economy to grind to a halt.

“This next step provides thousands of construction workers and businesses across the country with certainty at a time when they need it, and means that work can truly begin,” the HS2 minister, Andrew Stephenson, said.

Companies with HS2 contracts include Skanska Construction UK , Costain, Sir Robert McAlpine, Eiffage Genie Civil, Kier, Balfour Beatty and Vinci.

Companies will need to follow Public Health England’s guidance on social distancing at construction sites during the coronavirus outbreak, the Department for Transport said in its statement.

Preparatory work for HS2 has already started, such as clearing land and demolishing buildings, but to date no tracks have been laid.

In approving HS2, Johnson defied critics who said it was over budget and not necessary, showing his willingness to invest in infrastructure.

He said HS2 would slash journey times and add capacity to Britain’s crowded rail network, and help with his plan to “level up” the country by investing in transport links outside London.