As multiple lockdown measures are eased on 4 July, England will enter uncanny valley territory: life almost as we know it, but with notable exceptions. Weddings can go ahead at religious venues – but with a cap of 30 participants and no singing. Two households can meet indoors, but must make an effort to stay physically distanced. Hugs will have to wait for now. Playgrounds and pubs can open, but casinos and swimming pools will remain shut. So is the pick and mix of what we are and are not allowed to do driven by scientific predictions, common sense or just intended as a broad brush signal that the risk of infection has receded, but not entirely gone? The computer models, whose predictions about the pandemic’s trajectory paved the way for a nationwide lockdown in March, are not designed to give finely calibrated directions on the safest route back out again. They can’t say exactly whether 30 is the right number at which to cap celebrations for big life events. “For those sort of questions the models ran out of road some time ago, probably at the beginning of lockdown,” said Prof Mark Woolhouse, a member of Sage, but speaking in his academic capacity as an epidemiologist at the University of Edinburgh. “They cannot directly address policy questions at that level of granularity.” Instead, many of the latest judgement calls have been based on epidemiological evidence gathered during the pandemic. This has linked large gatherings such as weddings and religious services to a risk of outbreaks, making a restriction on size of meet-ups unsurprising. Clarity is also important. “There is nothing, as far as I know, magic in the number 30, but at least it’s something tangible for people to aim at,” said Ian Boyd, professor of biology at the University of St Andrews and a contributor to Sage. “It’s probably better than saying weddings should be as small as possible because some people will interpret that very loosely.” The decision to not permit singing during religious gatherings makes sense in the light of known outbreaks among choirs and the basic physics of how droplets spread. Under the new rules two households of any size will be able to meet outdoors or indoors, including overnight stays. People won’t be restricted to just one household, though. It will be possible to meet one set of grandparents one weekend, and the others the next, or in theory a different household every night of the week. The idea of banning large gatherings, but allowing a revolving door of guests might seem illogical. But scientists say that by staggering meet-ups it becomes far less likely that someone with Covid-19 will pass on the virus to members of multiple households during their infectious window. “An event of two households of 12 people is less of a risk than eight people all from different households,” said Woolhouse. So meetings of six people from multiple households have to happen outdoors, where the risk of transmission is considerably lower. The question of testing and tracing capacity also needs to be considered, and may have been factored in when deciding what reasonable limits were for how many people would be allowed to gather at one time. “If you can slow the number of contacts people make in any unit time, and if you get an outbreak, your chances of containing that using contact tracing is greater,” said Boyd. There is also simply the question of messaging. When Sage discussed how social contact might be steadily expanded – advice that underpinned the introduction of “support bubbles” for single-adult households earlier this month – the possibility of allowing set numbers of people or households to form larger bubbles was briefly considered. The group quickly dismissed such complex configurations because, they said, the rules would become fraught with confusion and could leave households faced with “potentially very conflictual and possibly irresolvable” decision about who to include in their list of allowed contacts. Some of the latest guidance has been questioned, however. Paul Hunter, professor in medicine at the University of East Anglia, said the recommendation that people maintain physical distancing while visiting – or even staying over – at another house appeared both unrealistic and unscientific. “How on earth that works in the house context is beyond me,” he said. “Sadly I don’t have an East wing of my property to put up guests. And the science behind that is actually quite poor.” He said that the continued focus on distancing irrespective of the length of time spent together was not in line with knowledge about how the virus spreads. “Staying 2 metres apart for two days while sleeping overnight in the same house is probably more risky than cuddling your grandchild for half an hour,” Hunter said. “There’s certainly some of the nuances that don’t seem to make sense to me when examined in isolation.” Overall, Boyd said, drawing up overarching guidance on how to ease the lockdown would be best described as “an art, not a science”. “It will be informed by an adaptive management method – try something which is approximately sensible based on the evidence and if you find it fails then ditch it and try something different,” he said.