The foreign secretary is the government’s so-called “designated survivor” and Johnson’s de facto deputy as first secretary of state, the PM’s official spokesperson said.
The spokesperson told reporters: “The prime minister is well.
“The foreign secretary [would take over]. The foreign secretary is the first secretary of state.
“The prime minister has the power to designate responsibilities to any of his ministers but now it’s the prime minister and then the foreign secretary.”
Meanwhile, the government is working on a package to help self-employed workers left out of pocket due to the pandemic amid criticism for failing to give them a proper safety net.
“We understand the difficult position the self employed are in,” the spokesman said.
“We have always said we will go further where we can and are actively considering further steps.
“We appreciate the urgency of the situation and officials are working around the clock to find a well targeted support package.”
Amid criticism for not introducing a tougher lockdown as some people appear to ignore government social distancing advice, the spokesman said the government was tracking a wide range of data to analyse whether its current policy is working.
This includes monitoring use of public transport, footfall in high streets, stations, parks and public spaces.
“If people are going out and socialising when they don’t need to then they are putting people’s lives at risk,” the spokesman said.
“If information which we are gathering shows that social interaction hasn’t stopped as we hoped it would, then we will need to take further measures.”
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No.10 also confirmed that the government would introduce an amendment to the emergency coronavirus bill on Monday to ensure its draconian powers have to be renewed every six months.
The spokesman said: “The measures in the bill are temporary, proportionate to the threat we face, and will only be used when strictly necessary.
“However we recognise the importance of parliamentary scrutiny and have heard concerns about the need for periodic reviews of the powers in the bill.
“We have therefore this morning tabled a government amendment to the bill to require the House of Commons to renew the legislation every six months.
“Should the Commons decline to renew the temporary provisions, the government will be required to bring forward regulations to ensure that they expire.
“The two-year time limit for the act overall remains in place, and not all of the measures will come into force immediately.”
Tuesday’s meeting of the cabinet will go ahead but a significant number of ministers will be taking part remotely using video or teleconferencing, the spokesman added.