Britain’s biggest trades unions have warned Boris Johnson that they will not recommend a return to work for their three million members until the government and employers agree a nationwide health and safety revolution as a result of the Covid-19 pandemic. In a letter to the Observer, leaders of the “big four” – Unison, Unite, the GMB and Usdaw – together with the Trades Union Congress, say many of their members have already lost their lives “transporting people and goods, protecting the public and caring for the vulnerable”. To minimise further deaths at work they are insisting that health and safety – something they say “used to be mocked by the free marketeers” – needs to be radically overhauled and stepped up in all workplaces if they are to back the government over easing, and eventually ending, the lockdown. The union leaders say that all employers should have to draw up and publish risk assessments and state what measures they have taken to make work safe for their employees. They also demand sanctions be imposed on rogue employers and call for government investment in health and safety inspections. “The trade union movement wants to be able to recommend the government’s back-to-work plans,” they say. “But for us to do that we need to ensure that ministers have listened and that we stay safe and save lives at work too.” Their intervention follows warnings from teaching unions on Friday that they will not support the reopening of schools until a system of “test, trace and isolate” is fully under way – something that is still some way off being fully operational. The letter is evidence of the dilemma facing the government as it tries to balance safety with getting as many people back to work as possible. In a speech tonight, the prime minister is expected to qualify the government’s “stay at home” message that has been central to its appeals to the public to adhere to the lockdown. It is understood that Johnson will say people can leave home to take exercise and fresh air more than the one time a day allowed at present. He will outline a route to gradual easing of restrictions when the infection rate allows, and announce plans for new guidance on safety at work. Some non-essential retail outlets, such as garden centres, will be allowed to reopen. However, Johnson will also announce some tightening of rules, including higher fines for people who flout lockdown instructions and plans to place people arriving on flights into UK airports in quarantine for 14 days. The prospect of these measures sparked immediate controversy, with the Airport Operators Association chief executive Karen Dee saying they would have a “devastating impact” on the aviation industry and the wider economy. The number of deaths from Covid-19 in the UK rose by 346 to 31,587 – still the highest of any European country. A separate figure, the number of deaths involving Covid-19 that have been registered, currently stands at 33,021. The true figure is believed to be much higher. Some 215,260 people have tested positive, an increase of 3,896 cases since Friday. A total of 96,878 tests were carried out on Friday, the sixth day running that the government has failed to reach its target of 100,000 tests a day. Last night scientists warned that it would be some time before new infections fell into the hundreds – the level they say is necessary to allow contact tracing and isolation to work effectively. Experts say the current level of 4,000 new cases a day would overwhelm the system. “Getting new cases down to a few hundred a day is a sensible ball park figure,” said Edinburgh University epidemiologist Professor Mark Woolhouse. “However, given the current rate of decline of Covid-19 infections it will be an awful long time before we get down to that level. And that is a real concern.” Some estimates suggest it could take a further six months of lockdown to cut new daily cases to their hundreds. Woolhouse said there were alternative approaches that could be taken. One would be for the government to introduce a new, very harsh version of lockdown like the one imposed in China. Another would be “to really get to grips with contact tracing,” according to Woolhouse, who is one of the UK’s leading experts on infectious diseases: “Otherwise I do not see how we are going to get any further forward and get out of this situation.” Downing St insisted Johnson was determined to proceed with “maximum caution” – despite mixed messages last week about a relaxation of measures from Monday. A No 10 source said: “This is a critical moment – so having assessed the evidence carefully, and scrutinised the data, the PM will address the public and ask for their resolve as we continue to do whatever is needed to defeat this devastating disease.” With polls showing the public anxious about ending the lockdown, and the unions increasingly worried about their members’ safety, businesses are said to be considering temperature tests for staff as part of the gradual return to work. Companies are also being warned about a spike in harassment claims as workers adjust to operating under social distancing rules. There are also concerns about the psychological impacts of returning to work, as well as a lack of awareness among employees about how to raise the alarm if they are being asked to work in unsafe conditions. A coalition of more than 250 charities and other organisations is calling on ministers to ensure that any easing of the lockdown doesn’t create new divisions in society. The Connection Coalition, which includes Age UK, Mind and the British Red Cross, warns that segmenting the population risks fracturing the united response that has brought communities together in response to the virus. A new Opinium poll for the Observer shows people in this country now view the UK as having performed worse than Italy, Spain and France in the Covid-19 crisis. Professor Ravi Gupta, a Cambridge University microbiologist, said that while maintaining lockdown for a few more weeks might still seem tempting, there were growing worries about the timing of a likely second wave of infection: “There is almost certainly going to be a second wave of Covid-19 cases after lockdown is lifted. That is inevitable though it remains to be seen how serious it will be. “However, the longer we leave the lifting of lockdown then it is inevitable that this second wave will occur later and later in the year. And we need to make sure we don’t let that happen in winter on top of the flu, norovirus and other outbreaks. “That means there is pressure for the government to think about lifting lockdown soon.”