Boris Johnson is expected to unveil a coronavirus warning system for England when he outlines his plans to gradually ease the lockdown. The prime minister will drop the “stay home” slogan and instead tell the country to “stay alert, control the virus and save lives” when he outlines his “roadmap” to a new normality during an address to the nation on Sunday. Johnson is planning to tell workers who cannot do their jobs from home to begin returning to their workplaces while following social distancing rules. It is understood that a warning system administered by a new “joint biosecurity centre” will detect local increases in infection rates, with the aim of altering restrictions locally in England. The alerts will range from green at level one to red at level five. Johnson is expected to say that the nation as a whole is close to moving down from four to three. The prime minister will chair a meeting of the emergency Cobra committee with cabinet ministers, leaders of the devolved nations and the mayor of London, Sadiq Khan, before his 7pm pre-recorded address. On Monday, the government will publish a 50-page document outlining the full plan to cautiously restart the economy to MPs. The shift in messaging will come amid concerns that workers may not wish to resume their roles after the firm instructions to “stay at home, protect the NHS, save lives”. The transport secretary, Grant Shapps, said on Saturday that the prime minister would be proceeding with “extreme caution”. The incoming changes for England were expected to be modest, he suggested, with a lifting of the limit of only one period of exercise per day and permission for garden centres to reopen. Shapps did not deny that ministers were planning to impose a 14-day quarantine on people arriving in the UK by plane from any country apart from the Republic of Ireland. He declined to address widespread calls for clarity, as some wondered whether the rule would apply to passengers arriving by boat and whether businesses would receive extra support because of fears the measure would be disastrous for industry. The minister did however address concerns that progress in the lockdown was being damaged, saying “throwing it away because it happens to be sunny outside this weekend, that would be absolutely tragic”. Johnson told the Sun on Sunday: “We’ll have to work even harder to get every step right … You have very few options on the climb up. But it’s on the descent you have to make sure you don’t run too fast, lose control and stumble.” Earlier, the Welsh first minister, Mark Drakeford, said the prime minister’s announcement for England would be “very much in line” with the “very smallest” easing granted in his nation. Schools in Wales would not be reopening to the majority of pupils in June, he added.