Boris Johnson is suffering a backlash over his plans to ditch rules on wearing face masks.
Doctors, regional mayors, trade unions and health charities are among those who have expressed fears over the relaxed measures.
Labour leader Sir Keir Starmer has also warned that lifting all restrictions in one go would be "reckless" - and is calling for face coverings to remain mandatory on public transport.
He said: "To throw off all protections at the same time when the infection rate is still going up is reckless.
"We need a balanced approach, we need to keep key protections in place, including masks, including ventilation and crucially... proper payments to those who need to self-isolate."
Dr Chaand Nagpaul of the British Medical Association said it was "increasingly concerning" for Mr Johnson to "decide to go full steam" on easing measures - despite warnings over rising hospital cases and deaths.
He urged ministers to ensure the wearing of masks is compulsory "until the rampant spread of infection has been brought under control and more of the population are fully vaccinated".
The government expects to push ahead with the final stage of the roadmap for ending lockdown measures on 19 July, and a concrete decision on whether to proceed will be taken next Monday.
If it goes ahead, people in England will be encouraged to use their personal judgement on the risks of infection - and they will be advised that wearing a mask can reduce the risk to themselves and others in environments such as crowded spaces.
Liverpool City Region mayor Steve Rotherham highlighted a YouGov poll that showed 71% of people wanted face masks to continue to be mandatory on public transport, as he tweeted: "The only opinions Boris Johnson seems to care about are those sat on his backbenches."
Greater Manchester mayor Andy Burnham and West Yorkshire mayor Tracy Brabin have also expressed concern at the ending of the legal requirement to wear masks on trains, trams and buses.
London mayor Sadiq Khan said further discussions would be held between the capital's transport bosses and the government, as he pointedly posted on Twitter: "My mask protects you, your mask protects me.
"The wearing of face coverings on public transport helps reduce the spread of COVID, and crucially gives Londoners confidence to travel - which is vital to our economic recovery."
UNISON assistant general secretary Jon Richards said that "removing most precautions at a stroke won't do anything to help reassure the thousands of nervous commuters who're due to return to their workplaces in a fortnight using crowded public transport".
And Lord Barwell, a Conservative peer who was former prime minister Theresa May's chief of staff, said: "The decision to make mask wearing voluntary on public transport is a mistake.
"If you want people to resume normal life, you need to make it feel as safe as possible for them to do so."
Tories who have campaigned to end the restrictions have welcomed the announcement, with some shouting "hallelujah" as Mr Javid set out the plans in the Commons.
Speaking at the Downing Street briefing yesterday, Mr Johnson also warned a further delay to ending lockdown measures would "run the risk of either opening up at a very difficult time when the virus has an edge" or "putting everything off to next year".
The prime minister added: "We must be honest with ourselves that if we can't reopen our society in the next few weeks, when we will be helped by the arrival of summer and by the school holidays, then we must ask ourselves: when will we be able to return to normal?"
Later today, Education Secretary Gavin Williamson is also expected to confirm that the "bubble" system in schools and colleges will also come to an end from 19 July.
Ministers have faced growing pressure to scrap these measures after figures showed the number of children off school due to COVID-19 in England is at its highest rate since schools reopened in March after the country's third national lockdown.
Over the last four months, since all pupils returned to classrooms, many children have faced spells of self-isolation after a member of their bubble - made up of a class or even whole year group - tested positive for coronavirus.
A Cabinet Office paper published yesterday said: "Early years settings, schools or colleges will not be required to routinely carry out contact tracing, which will help to minimise the number of children isolating.
"Contact tracing in specific educational settings would only be triggered if deemed necessary in response to a local outbreak."
Ministers also intend to exempt under-18s who are deemed to be close contacts of an infected person from the requirement to self-isolate, although these changes "are likely to come into effect later in the summer".
Health Secretary Sajid Javid is also expected to update MPs on further changes to contract tracing later today, and plans to ensure that fully vaccinated Britons no longer need to self-isolate if they are a contact of a positive case.