Starmer made the proposal in a speech in London, one day after Prime Minister Boris Johnson introduced his three-tiered regional alert plan designed to simplify and standardize the variety of COVID-related restrictions that have been imposed around the country.

But Starmer said Britain is in a decisive moment in the fight against the virus and “there’s no longer time to give this prime minister the benefit of the doubt.”

"This was not inevitable, but it is now necessary,” he said, acknowledging that the restrictions are largely unpopular.

He also said the lockdown idea comes from recommendations made by Britain’s Scientific Advisory Group for Emergencies (SAGE) which said “a package of stringent interventions is now urgently needed” to lower the rate of infection and take strain off hospitals and the National Health service.

Quoting SAGE, the opposition leader said, “not acting now will result in a very large epidemic with catastrophic consequences.”

Starmer proposed allowing only essential work and travel, restricting household mixing and that all pubs, bars and restaurants should be closed, but also be compensated. He said he understood the measures would require “significant sacrifices across the country.”

The Labor Party leader added that schools would not have to close under his proposal, as the lockdown would be timed to coincide with an upcoming school holiday.

Speaking directly to Prime Minister Johnson, Starmer said: “You know that the scientific evidence backs this approach ... that the restrictions that you introduced won't be enough.”

Starmer's words will only increase the pressure on the British leader, who has defended his decision not to re-introduce a full lockdown by saying he was trying to protect lives and livelihoods by balancing public health and the economy.