LONDON (BLOOMBERG) - Britain will survey 20,000 households in a bid to track the spread of the coronavirus, five weeks after it abandoned a strategy of community testing - a decision that left officials in the dark over the true spread of the disease.

The data will help scientists understand the rate of infection and how many people may have developed antibodies, the government said in an e-mailed statement on Thursday (April 23). Participants will form a representative sample of the British population and initial findings will be available in early May.

Prime Minister Boris Johnson's government has been criticised for not doing enough to trace the virus in the population, after the director-general of the World Health Organisation stressed that testing should be the "backbone" of the global response.

Though medics rigorously tracked the virus at the beginning of the outbreak and quarantined people as necessary, the government dropped the strategy on March 12 due to a lack of capacity and a belief that the disease had already spread too widely for it to be useful.

Britons face lengthy restrictions

The latest figures show more than 133,000 people have tested positive for the disease and 18,100 have died from it in hospitals - edging towards the 20,000 figure that the government said it would consider a good result, even before non-hospital deaths are included.

But officials have conceded they don't know the scale of the outbreak across the country, a blind spot that's complicating decision-making for ministers as they try to devise an exit strategy from a national lockdown that won't trigger a second wave of infections.

Chief Medical Officer Chris Whitty said on Wednesday that any relaxing of restrictions imposed on March 23 would still need to ensure the transmission rate remains below one, meaning each Covid-19 case is passed on to less than one other person.

He warned that at least some social distancing measures would likely need to remain for another year, or until an effective vaccine or drugs become available.

"As the transmission rate comes down, we need to get more data as to precisely where it is, in order to inform the measures we can actively consider," First Secretary of State Dominic Raab said on Wednesday when asked about how the lockdown might be lifted. "We've got to make sure we've got that evidence before we start touting around ideas."

Pressure is building on the government to outline how it plans to lift restrictions, even from members of Prime Minister Johnson's own Conservative Party.

"We need to start this discussion about how we get back to normality," Tory MP Geoffrey Clifton-Brown told BBC Radio on Thursday. "We have to, on behalf of the businesses of this country, begin to give them a little bit of hope as to when we might be able to get back to normality."

Health Secretary Matt Hancock told the House of Commons on Wednesday that Britain is planning widespread tracing of coronavirus patients and the people they meet as part of its exit strategy - though he also warned infection rates are still too high for the programme to work.

Mr Hancock told Parliament that a National Health Service app to assist with the so-called track and trace of cases is in "beta trials" which are "going well". The aim is to have a system in place within weeks, he said.

Countries including South Korea have been praised for using widespread contract tracing to limit the impact of the virus. The Times newspaper reported that thousands of people will be trained, including local council staff and civil servants, with Public Health England aiming to have the system up and running within three weeks.

"We are ramping up our testing capacity and our capacity for contact tracing in a matter of weeks, and we will have it ready to make sure that we can use that as and when the incidents of transmission come down," Mr Hancock told MPs. "Test, track and trace is a critical part of keeping the spread of this virus low."

Northern Ireland Secretary Brandon Lewis told the BBC nothing has yet been decided on how the programme would operate.