Labour has hailed a “welcome conversion” by Boris Johnson as Downing Street confirmed that the prime minister hopes to lead a public health drive, having blaming his stint in intensive care on obesity. The prime minister was hospitalised with coronavirus last month and spent several nights in intensive care at St Thomas’s hospital in London. Several slimmer colleagues, including the health secretary, Matt Hancock, and Johnson’s chief adviser, Dominic Cummings, escaped with milder symptoms. Asked about reports that Johnson had joked with aides that “thinnies” are not as prone to the worst effects of the coronavirus and now wants to lead a “war on fat”, his official spokesman said: “As we outlined in our recovery strategy, this government will invest in preventive and personalised solutions to ill health, helping people to live healthier and more active lives. “You have heard the PM speak on a number of occasions about the importance he attaches to cycling.” The shadow health secretary, Jon Ashworth, said: “We’ve repeatedly warned of the long-term health risks of obesity. If the prime minister now supports extending the sugar tax and banning junk food advertising before the watershed, then that’s a welcome conversion. We are facing an obesity crisis, and decisive action is urgently needed.” However, No 10 denied that Johnson was considering increasing the sugar tax – the levy imposed by George Osborne to encourage food companies to reformulate their products. That would have been be a considerable turnaround from Johnson’s stance during last year’s Tory leadership contest, when he announced a moratorium on “sin taxes”, claiming that they hit the poorest consumers hardest. Johnson has generally been against “nanny state” interventions in the public’s daily lives, an instinct some critics blamed for the government’s reluctance to take draconian lockdown measures in the early stages of the coronavirus crisis. The government has not so far enacted plans set out in a green paper on preventive health in the final days of Theresa May’s premiership, which included consulting on a ban on junk food advertising before 9pm. Early research has suggested that obesity may be a significant factor in determining the severity of Covid-19 cases. Johnson’s spokesman said the government was examining the importance of this and other criteria. “It is critical to understand how factors such as ethnicity, deprivation, age, gender and obesity could be disproportionately impacting how people are affected by coronavirus,” he said. “Public Health England launched a review into the factors affecting health outcomes from coronavirus, to include ethnicity, gender and obesity, and this will be published by the end of May,” he added. The outcome could help the government tailor its advice to different groups during the coming months as the search for a vaccine continues. Several officials have said Johnson is entirely serious about the plan to improve public health, and is particularly focused on pushing through plans to get more people walking and cycling. One issue with this has been to ensure local authorities take the necessary action, but if central government provides financial support to regional transport systems, as has happened with Transport for London, the hope is that pressure can be exerted for rapid progress. As well as improving public health, the government is keen to ensure that as many people as possible who are returning to work as the lockdown eases avoid public transport. The transport secretary, Grant Shapps, announced the allocation of £2bn of his department’s budget last week for creating “emergency” cycle lanes, widening pavements and other interventions aimed at encouraging the public to get around using “active travel”.