As the UK coronavirus outbreak continues to grow, the Prime Minister’s spokesman confirmed that the Foreign Secretary would step in if necessary if Mr Johnson fell ill.
The spokesman said: “The Prime Minister is well… the Foreign Secretary is the First Secretary of State.”
If Mr Raab was also ill, the Prime Minister has the power to delegate responsibility to any of his ministers, the spokesman added.
Reports over the weekend suggested a number of ministers were jockeying for the post of stand-in prime minister.
It comes as the Government continues to battle the coronavirus outbreak, with 5,683 cases of Covid-19 now being confirmed in the UK.
Mr Johnson has no symptoms of the virus and Mr Raab has tested negative twice after developing a cough.
Members of Boris Johnson’s Cabinet will steer clear of Downing Street in order to comply with social distancing measures, the Prime Minister’s spokesman added.
He said Tuesday’s Cabinet meeting will see a “very significant” number of ministers taking part remotely.
“I would expect that now and for the foreseeable future a very significant number of Cabinet ministers will take part by dialling in or via video conferencing,” the spokesman said.
The Government will also ramp up its public information campaign, Downing Street said.
“We have been conducting an extensive public information campaign on social distancing measures,” the Prime Minister’s spokesman said.
“I think you could expect much more information to be made available to the public in the coming days as well.”