However,with Johnson remaining conscious,it remains unclear as to whether his most significant powers,such as issues of national security,had been transferred to Raab.
Britain's Foreign Secretary Dominic Raab leaves a meeting in Downing Street,London.Credit:PA
Leading the daily Downing Street press conference on Monday afternoon,Raab said that a team of ministers and Whitehall officials were working"full throttle"to carry out the instructions of Johnson from his hospital bed at St Thomas's,central London.
But when asked whether he had taken over Johnson's"security responsibilities"Raab declined to comment.
"We are getting on with all of the various strands of work to make sure at home and abroad we can defeat the virus and pull the country through coronavirus and the challenges that undoubtedly we're facing at the moment,"Raab said.
Earlier,Raab said he had not spoken to the Prime minister since Saturday but it is understood the pair communicated shortly before Johnson was taken into the ICU when Johnson asked Raab to deputise.
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The UK's undefined chain of command stands in contrast to the United States,where it is set out in the constitution.
The powers and responsibilities of the US vice president are clearly defined,whereas in the UK the office of deputy prime minister has not been used since Nick Clegg entered into the coalition with David Cameron in 2010.
Even before the Prime Minister's admission to hospital,the confusion had already given rise to reports of infighting among Cabinet ministers,with allies of Michael Gove,the Chancellor of the Duchy of Lancaster,suggesting that he was next in line.
As the coronavirus outbreak escalated,Downing Street foresaw the potential constitutional dilemma and began drawing up a"designated successor"plan"with Raab nominated as first recipient.
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But even last night,the extent of his powers remained uncertain,with Dr Catherine Haddon,a senior fellow at the Institute for Government,indicating that some powers could be distributed to a number of Cabinet ministers.
"The power would derive from the Prime Minister saying who he wants ministries to respond to,"she toldThe Daily Telegraph. These could include authority over the UK's national security apparatus,such as control of the nuclear launch codes.
"Certainly in the Cold War and the years after,prime ministers would authorise nuclear deputies who were named Cabinet ministers,who in the event of something happening would then be called upon if the prime minister was in that moment unavailable.
"It's not so much like America where they have to carry the nuclear codes around,it's just making sure there is a chain of command if the Prime Minister were not available at that moment."
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Dr Haddon also indicated that oversight of Britain's intelligence agencies could become a shared ministerial responsibility.
"MI5 reports to the Home Secretary,MI6 and GCHQ report to the Foreign Secretary,so there are still lines of communication,"she said.
"The Prime Minister deals with them all directly and gets daily intelligence briefings,but so do other Cabinet ministers,who also have some degree of oversight powers. The Prime Minister is the ultimate authority,but that doesn't mean he's the only one he engages with them."
Who is Dominic Raab?
Raab,46,ran against Johnson to become leader of the Conservative Party and prime minister in 2019. During that campaign he criticised Johnson’s “bluff and bluster” over Britain’s exit from the European Union.
Britain's Foreign Secretary Dominic Raab shelters from the rain in Sydney,in February,at a visit to the British-Swedish multinational biopharmaceutical company,AstraZeneca.Credit:AP
Raab was eliminated midway through the contest and then endorsed Johnson.
He was appointed as foreign minister in Johnson’s first cabinet after the prime minister took office in July 2019. Raab is a hardline eurosceptic,who has long campaigned for Britain to leave the EU.
The son of a Czech-born Jewish refugee who fled the Nazis in 1938,Raab was brought up in the southern English region of Buckinghamshire and studied law at Oxford University before becoming a lawyer working on project finance,international litigation and competition law.
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Before entering parliament in 2010 Raab also worked for Britain’s diplomatic service including a posting in The Hague working on bringing war criminals to justice. He also advised the government on the Arab-Israeli conflict and counter-terrorism.
A karate black belt,he served briefly as Brexit minister under then-prime minister Theresa May before quitting in protest at her proposed deal to leave the EU.
While Brexit minister he was derided for saying that he hadn’t fully realised how reliant Britain was on the Dover-Calais ferry crossing for trade. The route is one of Britain’s busiest and most important links with continental Europe.