The rumours began a week after Boris Johnson began self-isolating in the flat above No 11 Downing Street. The story, spread by the prime minister and his aides, had thus far been reassuring. Yes, he had Covid-19. But the symptoms were nothing to worry about. Mild even. And at a time when deaths from the pandemic were continuing to climb, Johnson had a firm grip on the crisis and the machinery of power. All of this changed on Thursday 2 April. At the lunchtime briefing for lobby correspondents, Downing Street stuck to this soothing script. The prime minister continued to have a temperature. But, subject to medical review, there was every prospect he would be able to emerge from isolation the next day, the press was assured. Seemingly, Johnson had shaken off the virus with the same alacrity as the health secretary, Matt Hancock, back after a short interlude. But that did not happen. Over the next five days the public were taken on an emotional rollercoaster; a prime minister who was apparently in good spirits and working hard, was then in an intensive care unit (ICU) and in real danger of “taking one for the team”, as his father, Stanley, would put it. A Guardian analysis of what was said in public suggests the relentlessly upbeat pronouncements from Downing Street were at odds with what was known in private. A lack of candour at a time of national crisis? It wouldn’t be the first time ... Behind the scenes, colleagues were painting a more alarming picture of Johnson’s health at the end of his first week of sickness. He did indeed have a fever. Left unmentioned, however, was his persistent cough: an unmistakeable splutter. During cabinet video conferences the prime minister’s symptoms were painfully evident. They confirmed the growing seriousness of his condition. One source suggested the prime minister was coughing up blood. Not true, Downing Street said. Covid-19 can take different forms. Many people who catch it scarcely notice. Others grow critically ill. Those with even moderate symptoms can experience chest pains, headaches, cold spasms and extreme fatigue. The disease is novel. Clinical experts agree that the most dangerous phase is week two. Then patients generally start to recover. But some precipitously crash, as the virus attacks the lungs. By 2 April, doctors were worried that in Johnson’s case, the infection was taking this second, ominous path. St Thomas’ hospital – just across the Thames from Downing Street – began making preparations to admit the prime minister. According to one source, staff were told his condition was significantly worse than had been publicly admitted – really bad, in fact. And that he was likely to need oxygen support. Inside Downing Street, Johnson was in contact with his principal private secretary, Martin Reynolds, and his GP. Many of his usual advisers were themselves off sick, with Dominic Cummings at home self-isolating and the director of communications, Lee Cain, away. As Johnson’s condition steadily worsened, phone calls were cut down, government papers trimmed. His approach to his illness was characteristically upbeat: he would vanquish it. Stories of Johnson’s decline were now circulating among Tory backbenchers and journalists. Downing Street insisted these whispers were wrong. In hindsight, this guidance seems misleading. The rumours were loosely right: the prime minister was seriously unwell, more than admitted. Perhaps Johnson was minimising how bad he was feeling, even to those in his inner circle? At 8pm that evening the prime minister emerged on the steps of No 11, to clap for NHS workers. He looked terrible. The next day, Friday 3 April, Johnson recorded a video in which he urged the public to stay at home during the forthcoming sunny weekend. He said he still had a temperature and was staying in isolation. It was day eight. In fact, Johnson was sinking in classic Covid-19 fashion. By the weekend it was becoming clear to the few in contact with him that the prime minister was struggling to do his job. On Saturday 4 April, Johnson’s fiancee, Carrie Symonds – pregnant and self-isolating with coronavirus symptoms – grew agitated, friends said, crying down the phone. Hancock claimed all was well, telling Sky News on Sunday morning the prime minister was “working away” and had his “hand on the tiller”. In reality, Johnson’s breathing had deteriorated. On Sunday afternoon the plan to admit Johnson to St Thomas’ was rebooted. That evening he was driven across the Thames and taken to a private room on the 12th floor. Downing Street did not deny reports he was immediately given oxygen. Once again, his spokesman sought to downplay events, saying this was “a precautionary step”. The consultant in charge of the prime minister’s care was Dr Richard Leach, the clinical director of the hospital’s pulmonary team and a leading lung expert. The following day, Monday 6 April, things took an almost Soviet turn. While the prime minister was gasping for breath, aides insisted at a lunchtime press briefing that he was busy working his way through red boxes. At 5pm the foreign secretary, Dominic Raab, even claimed Johnson was in charge and “leading”. Asked when he had last spoken to him, however, Raab replied it had been Saturday. It appeared the government was covering up, or incompetent, or both. (No 10 says when Raab spoke he was unaware of his boss’s sudden decline.) On Monday afternoon the prime minister’s condition got significantly worse. A decision was made to transfer him to one of St Thomas’ two intensive care units. Johnson was put in a side room, on the east wing’s first floor. The development stunned Downing Street. At 8.10pm it announced the prime minister was in critical care, saying he had asked Raab to deputise for him. The fiction of Johnson being in command had ended. World leaders and politicians sent him good wishes. His aides were knocked over, distraught. Typically, Covid-19 patients in ICU are put on ventilators. This is an invasive and traumatic process. Some hospitals prefer to treat severe cases with a continuous positive airway pressure ventilator (Cpap). St Thomas’, however, favours full ventilation, believing this is how you save people, specialists say. One source inside the hospital said Johnson was “very sick” when taken into ICU. “It was touch and go whether he would be put on a ventilator,” the source said. The same source, however, wonders whether the prime minister really should have been in intensive care. About 130 other patients were in critical care at the time, the vast majority hooked up to ventilators. At no point was Johnson on a ventilator. Nor did he receive Cpap, a less invasive form of treatment. The source said: “Before the coronavirus crisis you could be in ICU without being on a ventilator but pretty much every bed is now taken by a coronavirus patient with a ventilator. I know people who work in ICU and I know the technicians who prepare all the equipment and they all say he was not put on a ventilator. He was taking up an ICU bed when he didn’t need it. The idea that you would put a patient who didn’t need a ventilator on an ICU bed is nonsense.” Weighed against this was the fact that Johnson – who is 55 – fitted the pattern of other serious male cases. As a second source put it bluntly: “They have a very low threshold for people of his profile (over 50, fat). If they don’t get a tube in early it makes it much harder to do later on, if he deteriorates further.” Back in Whitehall, a new protocol for briefing on the prime minister’s health was set up. Only limited updates from St Thomas’ would be passed on. Johnson was stable and being monitored, No 10 said. On Wednesday 8 April there was tentative good news. Johnson was still not on a ventilator. “If they don’t go on one in the first 48 hours of being in ICU it’s usually a good sign,” the second source said. At the daily briefing the chancellor, Rishi Sunak, revealed the prime minister was sitting up and engaging positively. According to hospital insiders, he was reverting to his old self. “He’s charming all the nurses, insisting they call him ‘Boris’,” one reported. After three days in intensive care he was moved on to a general ward. Downing Street said he was in extremely good spirits and “enormously grateful” for the care he’d received. Symonds tweeted a painting of a rainbow with 26 clapping emojis. There were grim questions still, such as how long would his recuperation last and had the virus caused long-term damage to his health and lung capacity? By Easter weekend Johnson was keen to go home. His medical team counselled caution. According to one source they advised him to stay in a little longer, until 14 April. Johnson prevailed. At midday on Sunday, he was discharged, following seven nights in hospital, three of them in intensive care. Hours later, Johnson appeared in a video message sent from Chequers, his prime ministerial retreat in Buckinghamshire. It was vintage Johnson. Dressed in a suit and tie, he declared the NHS had saved his life “no question”. He paid tribute to two nurses who had watched over him for 48 hours in intensive care when “things could have gone either way” – Jenny from New Zealand and Luis from Portugal. He said their care was “the reason in the end my body did start to get enough oxygen”. Johnson had experienced a scare, no doubt about that. One specialist said he thought the prime minister had gilded the lily a bit – “I suspect there’s been an element of poetic licence there” – but at the same time stressed that he did need oxygen, albeit through a face mask rather than Cpap or full mechanical ventilation. The specialist did not begrudge Johnson being put into ICU, reasoning “he’s the prime minister”, and “without that oxygen he would not have got better”. The saga had a curious footnote. Photographs taken from a public footpath showed Johnson and Symonds walking with their dog in the grounds of Chequers, the prime minister bundled up in a duffel coat and gloves. He looked pale but well enough to go for a stroll. Most ICU patients leave hospital in a wheelchair. They suffer from exhaustion, muscle wastage and other chronic problems. The prime minister appears to be in much better shape. Johnson won the 2016 EU referendum by combining support for the NHS – the UK’s unofficial religion – with soft nationalism and Brexit. Whatever mistakes have been made over the pandemic, Johnson now has another winning political formula to silence his critics: without the NHS I wouldn’t be here.