The white square block of St Thomas’s hospital sits on the banks of the Thames, right across Westminster Bridge from the House of Commons. The hubbub of cameras in front of its door since Boris Johnson was admitted as a patient on Sunday signals that in Britain, the coronavirus emergency has moved into a new, deeply concerning phase.With the further news on Monday that the Prime Minister had been taken into intensive care, the Government issued a statement that he had given Dominic Raab, the foreign secretary, the authority to deputise for him “when necessary”. That careful qualification — entirely in line with the ambiguities of power in the British Constitution — has plunged the country into wondering just how much authority Raab has.For a few weeks, he may be able to dodge big questions. The scale of the managerial task — of getting equipment to the National Health Service and money to the suddenly unemployed — is itself all but overwhelming. But before Johnson was taken into hospital, the Government was under growing pressure to explain how it will lead the country out of the lockdown. That is not a question that Raab and his Cabinet colleagues can duck for long.The Prime Minister’s hospitalisation — after a week of coronavirus symptoms, during which he was isolated in his apartment on Downing Street — has for the moment quieted some of the growing criticism of the Government’s response to the coronavirus. A messy start, with many changes of tactics, meant the Government closed schools, cafés and businesses weeks after Italy, France and Spain did, despite the spectacle of rising death tolls there.But it then did two big things right, and fast. Johnson spoke to the nation in announcing the near-lockdown, with his clearest message which has since become the slogan “Stay Home, Protect the NHS, Save Lives”.He also endorsed his chancellor, Rishi Sunak, in a rapid bailout of the economy and support for the imminently unemployed or furloughed, which included £55 billion (about $68 billion) of extra public spending and tax cuts, and a further £330 billion — or 15 per cent — of GDP in loan guarantees. It is also allowing people to pay taxes late, which is worth about £40 billion. Within this, the Government is paying 80 per cent of the wages of those put on furlough, and it came up with a separate package for the self-employed — who have fuelled much of the “gig economy” growth of the past ten years — offering to pay 80 per cent of their average profits for the past three years.The extreme centralisation of the British Government and institutions has also arguably worked to its advantage. The Bank of England and Treasury worked well together. The “devolved nations”, as Scotland, Northern Ireland and Wales are called in Westminster jargon, have considerable freedom over health policy, but they have united in the joint briefings to pull together with the central British government.The NHS, raised in this crisis to the status of the nation’s unifying religion, can be unwieldy and hard for Downing Street to influence — as some of the problems in getting protective equipment and virus tests to its hospitals have shown. On the other hand, it is consistent in its approach, extending its care to every citizen in the country, now including the Prime Minister. That universal embrace has been rewarded with renewed national adoration in this crisis, people coming out on their front steps on Thursday evenings at 8pm to clap their gratitude for the risk its workers are running.A much pilloried system of social benefits — called Universal Credit — which has been plagued with problems in its development, has also come into its own. It replaced a system with six separate benefits; now, people have to sign on only once, and this seems to have made using the system to distribute support quickly far easier — although the coming weeks are bound to reveal glitches.That means that Raab’s most immediate challenge is simply how to implement these big decisions that the Government made when Johnson was well. He needs to get more protective equipment out to frontline NHS workers; public opinion will not be forgiving if they die avoidable deaths for lack of protection. And he needs to make sense of the testing regime, an area where Britain lags behind other countries. Yet the pledge of 100,000 tests a day by the end of April was a rash one, given the problems that all countries are finding in securing reliable tests.Bigger decisions loom, though. Before the Prime Minister became so seriously ill, there was a rising chorus questioning whether the cure was becoming more damaging than the affliction — particularly for younger people, hit hard by the economic shutdown and comparatively lightly touched by Covid-19. More people, including Members of Parliament and the new leader of the Labour opposition, Keir Starmer, were asking what the Government’s “exit strategy” from the lockdown would be.In a sense, this is unfair: no government on the planet has an exit strategy, nor will there be a clear one until a vaccine is available. But the three-week review of Britain’s lockdown is due next week. Raab may be able to defer that, given scientific advice that the nation has no sign of having reached the peak. But at some point, he and the Cabinet will have to confront it.This is where the ambiguities of Britain’s famously unmodified constitution kick in. Raab has the authority delegated to him by the Prime Minister, but that does not come with the formal powers that the Vice-President of the United States would have. Britain is governed by the Cabinet, which takes collective responsibility for decisions. The Prime Minister is “first among equals” but acts with the support of the Cabinet — and falls, ultimately, without it.Raab can do only what his Cabinet colleagues support him in doing. For the moment, that is simply to execute the strategy that Johnson has laid down. But soon, there will come a time when the Government needs to make bigger decisions. If the Prime Minister cannot, the Cabinet will have to do it without him. No surprise, then, that there are calls this week for Britain’s rules of succession and delegation finally to get formalised and written down.• Bronwen Maddox is the director of the Institute for Government, a London think-tank