Labour leader Sir Keir Starmer is urging the government to publish an exit strategy from the coronavirus lockdown this week.
The government is expected to announce on Thursday that social distancing measures will continue.
Sir Keir said Labour would back such a move but to maintain public trust “there needs to be transparency”.
The government said talking about an exit before the virus had reached its peak risks confusing the public.
The Labour leader has written to Dominic Raab, who is deputising for Prime Minister Boris Johnson while he continues his recovery from coronavirus, to say Labour would support a continuation of the measures.
But, he said, the government needed to set out an exit strategy to maintain trust and to ensure that arrangements are in place for it.
“We’ve got to have the trust of the public,” Sir Keir told BBC Radio 4’s Today programme, adding that it was “inevitable that the lockdown will have to continue”.
“For that trust there needs to be transparency and openness – they need to know what the thinking is on when lockdown will end.”
He said that government planning was previously not quick enough, and said, “let’s not repeat that”.
“Mass testing and then tracing is likely to be amongst the options for ending the lockdown,” Sir Keir said.
“If that is right we need the government to say so because decisions need to be taken now to make sure that the number of tests that are needed and that the arrangements are in place so they can be implemented at the relevant time.”
He said that he believed “in principle” schools should be amongst the first institutions to restart following easing of lockdown measures.
In an interview with BBC Breakfast, however, Sir Keir said it would be “wrong” to put a time on when schools should reopen.
“Until we know the curve is flattening, then I’m afraid we have to stay in the conditions we’re in,” he said.
In his letter to Mr Raab, Sir Keir said millions of people had “played their part” and made sacrifices and “in return, the government needs to be open and transparent with the public about how it believes the lockdown will ease and eventually end”.
Sir Keir warned the “silent pressures” on communities across the UK “cannot be underestimated”, and said that to maintain morale and hope “people need a sense of what comes next”.
A government source said: “Our strategy is focused on saving lives. We have been clear that all decisions will be guided by the scientific advice and data.
“Talk of an exit strategy before we have reached the peak risks confusing the critical message that people need to stay at home in order to protect our NHS and save lives.”
Former chancellor Sajid Javid told the Today programme that the government’s first “duty” was to “protect the public” and that lockdown was the “right policy because it’s based on scientific and medical advice”.
But, he said, it was “premature” to set out an exit strategy at this point.
The government has previously indicated that work is under way on a plan to lift restrictions, but no details have been published.
Speaking on Tuesday at the Downing Street daily press conference, Chancellor Rishi Sunak insisted the government’s priority would remain saving lives.
And he warned that the government will not be able to protect every UK business and every household during the pandemic but if ministers had not taken the actions they had, “the situation would be much worse”.
NHS England’s Medical Director, Prof Stephen Powis, told the news conference lockdown compliance levels among the public were “very high” and this was beginning to have an impact on hospital admissions,
“We need to keep it that way. We absolutely need to make sure that we keep the benefits of this going forward and we don’t take a foot off the pedal, we don’t become complacent,” he added.
It comes as the Office for Budget Responsibility predicted the UK economy could shrink 35% between April and June, while unemployment surges by more than two million.
But it predicted a sharp bounce back, with GDP likely to jump 25% in the third quarter and a further 20% in the final three months of 2020.
The watchdog based its calculations on a three-month lockdown followed by a partial lifting for three months.