The Johnson government has backtracked on the use of masks after remaining coronavirus restrictions are lifted in England on July 19, with a senior minister saying they should still be worn indoors as case numbers continue to rise sharply.

Boris Johnson is expected to announce on Monday that “step four” of lockdown easing will go ahead next week, despite concerns from scientists that hospitals may be overwhelmed this summer. On Sunday, another 31,772 cases of coronavirus were reported along with 26 deaths.

The prime minister will host a Downing Street press conference on Monday to announce the final relaxation of rules. On Sunday he struck a cautious tone, acknowledging that the link between cases and hospitalisations had been “weakened” but not entirely broken.

“We are tantalisingly close to the final milestone in our road map out of lockdown, but the plan to restore our freedoms must come with a warning,” he said, noting that “the global pandemic is not over yet” despite the success of the vaccination programme.

“Cases will rise as we unlock, so as we confirm our plans our message will be clear. Caution is absolutely vital, and we must all take responsibility so we don’t undo our progress, ensuring we continue to protect our NHS.”

The government’s decision to press ahead with easing comes as it has changed it stance on masks. Johnson had previously said wearing masks in England would be a “personal choice” and the government would end the “legal obligation to wear a face covering”.

But Nadhim Zahawi, vaccines minister, on Sunday took a different stance to Johnson, suggesting the government would advise people to act more cautiously. He told Sky News that the government was likely to still recommend masks after the legal obligations ceased.

“It’s important that we remain cautious and careful and the guidelines that we will set out tomorrow will demonstrate that, including guidelines that people are expected to wear masks in indoor enclosed spaces and, of course, to remain vigilant with hands and face,” he said.

Zahawi also told the BBC that Johnson would emphasise caution when announcing that the final restrictions would end on July 19. “The guidelines will be very clear on things like mask wearing. There’s an expectation indoors, in crowded places and on public transport.”

The opposition Labour party has called for masks to be mandatory on public transport. Kate Green, shadow education secretary, on Sunday described the government’s policy as a “recipe for confusion”.

Johnson’s decision to press ahead with the easing of lockdown restrictions despite rapidly rising cases and hospital admissions was reiterated by the health secretary Sajid Javid, who said hospital waiting lists could rise to 13m as a result of extra pressure on the NHS.

Javid told the Sunday Telegraph newspaper he was “confident” the July 19 easing would go ahead, but he was “shocked” that waiting lists could increase significantly.

“What shocked me the most is when I was told that the waiting list is going to get a lot worse before it gets better,” he said. “Hearing that figure of 13m, it has absolutely totally focused my mind, and it’s going to be one of my top priorities to deal with because we can’t have that.”

Javid said dealing with the backlog, which is currently about 5.3m patients, was a top priority and pledged to clear it “as quickly as possible”. But he warned it would take a “considerable time to clear”.

Meanwhile, Zahawi downplayed reports suggesting Downing Street was seeking to reduce the gap between first and second vaccine doses from eight to four weeks.