Dominic Raab will run the country if Boris Johnson is struck down by coronavirus as “designated survivor” plans are drawn up, Downing Street says.

No 10 stressed the prime minister is “well”, but when asked who would take charge if he became incapacitated, replied: “The foreign secretary is the first secretary of state.”

The clarification comes after reports that some ministers have been pushing for Michael Gove, the cabinet office minister and key Johnson ally, to take over if necessary – rather than Mr Raab.

The prime minister – unlike Donald Trump – is not believed to have been tested for coronavirus, but is thought to be at higher risk because of regular, intense meetings to combat the crisis.

Westminster has been identified as a virus hotspot, with several dozen MPs now in isolation and expectations that parliament will soon be shut down.

Mr Raab, Mr Gove, the chancellor Rishi Sunak, and Matt Hancock, the health secretary, each chair a committee coordinating different parts of the government’s response.

Successive prime ministers have resisted pressure to set out a formal procedure for what happens if someone else is required to take over.

Peter Bone, a Conservative backbencher, has tried to pass a law without success and said, on Sunday: “Nobody seems to be able to tell me what happens if the prime minister is incapacitated.

“In a national emergency, you don’t want to be scrabbling around worrying about who’s in charge. And you don’t want the foreign secretary and the cabinet office minister arguing about who’s in charge.”

As the crisis escalates, Downing Street has been forced to play down reported tensions between Mr Gove and Mr Hancock, who is leading the NHS response.

Mr Raab has, so far, been the face of efforts to help up to a million Britons stranded abroad, facing criticism for insisting it is impossible for the government to lay on repatriation flights.

He also came under fire for claiming the pandemic strengthened the case for completing Brexit at the end of the year – even as an extended transition period appears increasingly inevitable.

The prime minister’s spokesperson declined to set out any further detail of the “designated survivor” plans, but stressed the flexibility available to him.