England’s coronavirus lockdown should not be further lifted until the government’s contact-tracing system has proven to be “robust and effective”, the World Health Organization has said after widespread criticism of the first results of the new tracking operation. As shops across England prepared to reopen, and people were encouraged by the government to come out of their homes and on to the high street, Dr Hans Kluge, the WHO’s director for Europe, cautioned that the UK remained in a “very active phase of the pandemic”. His remarks came as ministers confirmed a review of the 2-metre distancing rule, with the government coming under pressure from business leaders, Tory backbenchers and rightwing media to further ease the lockdown. Boris Johnson said on Sunday that the falling numbers of coronavirus cases has given the government “more margin for manoeuvre” in easing the 2-metre physical distancing rule. In response to data showing the government had failed to trace the contacts of a third of those testing positive in the first week of the new system, Kluge warned in an interview with the Guardian against rushing into reopening the economy. The WHO official said the tracking in England of about 31,000 contacts of 8,000 infected people was encouraging and a cause for congratulations. But he added that Downing Street needed to be convinced it could “aggressively” track infections as the prime minister looks to reopen the economy. As of Saturday there were 41,662 deaths in the UK – a daily increase of 1,425 confirmed cases and 181 deaths. Governments who locked down early in the pandemic, in the face of public criticism, had recorded fewer deaths during the pandemic, Kluge said, but European leaders would now be judged on their management of their exit from the restrictions. “We know that early lockdowns saved lives and bought some time for the health system to be ready,” Kluge said when asked about the British government’s record. “But I would rather than instead of looking to the past, jump to the future and say that the question of lifting the lockdown is as important as going to the lockdown. The key words here are to do it gradually. Do it carefully. “Contact tracing is key especially as the UK starts to relax the social and physical distancing measures. There has to be a robust track-and-trace system in place of operation. I would like to reply [to questions about the first results of the system] and say we need an effective tracking system in place, it is one of the measures that we recommend that are in place now. One certainty is that a country has to decide themselves on that one.” On Thursday, Dido Harding, the chair of the NHS test-and-trace service, admitted that the UK’s scheme – billed as “world-beating” by Boris Johnson – would need to improve. Of the 8,117 positive cases referred to contact tracers, 5,407 had been willing to hand over the names and phone numbers of people they had met in the previous two days. Despite the stumbling start and the lack of a promised coronavirus app slated for launch by the end of May, Johnson is under growing pressure from Conservative backbenchers to push on with lifting the lockdown amid grim forecasts of mass unemployment. “We know that the situation in the UK is still being taken very seriously,” Kluge said. “But we also know that it is a balance between three factors: population health, economic and social, and the third is the wellbeing of the people. So whatever the country decides: be ready. It is not over. And whatever decision you make, please make sure it is based on public health and epidemiological observations.” Kluge said international comparisons were difficult but that the pandemic had shown the importance of governments being able to communicate effectively with the public to convince them of the necessity of respecting the unprecedented nature of the requests being made. Noting that Downing Street had delayed going into lockdown in early March for fear that the population would fail to follow the rules with rigour as the restrictions dragged on, Kluge said: “What is the lesson there? Keep people engaged.” Kluge said he could understand the government’s caution despite calls from senior Conservatives, including the former leader, Iain Duncan Smith, for a rethink on the 2-metre guidance. Johnson has ordered a review of the policy to be completed by July. “Every country has their own context, based on a risk assessment. In the UK I would say this is a very active phase in the pandemic so, more let’s say, careful,” he said. “There is no right or wrong. Of course, ideally, it would be everywhere the same but countries are doing this based on their own risk assessment … “Whether it’s one or two metre is less important than the fact that people will adhere to the measures, to the physical distancing, to the handwashing, to the respiratory hygiene, and that they understand that it’s not over. This is the key issue.” With Europeans eyeing up the potential of summer holidays, Kluge said Europe as a whole could not be complacent, with infection rates increasing in the past fortnight in Albania, Armenia, Azerbaijan, Bosnia and Herzegovina, and North Macedonia. The Europe region within Kluge’s remit is made up of 53 countries: the UK, the member states of the EU, and the countries of central and eastern Europe including Turkey and Russia. The reopening of schools had led to some local flare-ups in Europe that were swiftly contained, Kluge said, and the continent could face a deadly combination of a second wave of coronavirus and an influenza pandemic in the autumn. “We call it when ‘Covid will meet the flu’,” Kluge said. “The issue is that several epidemics can go together and how do you have policies in place? We put an expert group together to look at that because no one has the ideal answer.” Kluge said it would be crucial for governments to distribute the influenza vaccine among the groups most vulnerable to Covid-19: older people, men, and generally people with underlying conditions such as cardiovascular disease, diabetes and renal disease. There are 135 potential vaccine candidates for Covid-19, of which 10 are in clinical trial. Kluge said it “may well take a year, a year and a half now” before a vaccine could be ready. “My understanding is that it’s still a bit early in the day. Of course one thing is efficacy, but then the other one is safety … We are hopeful and there’s a lot of effort. But, until that moment, let’s implement what we know works.”