Government scientists have said "stronger" restrictions could be needed this autumn and winter, despite promises of an "irreversible" route out of lockdown. 

Newly released papers from the Scientific Advisory Group for Emergencies (Sage) show ministers were urged to keep "baseline" restrictions such as face masks and working from home, and warn that new freedoms could create "superspreader" events.

The tranche of papers, released as Boris Johnson announced the next steps out of lockdown, suggest opposition from Sage to a "big bang" lifting of policies.

Boris Johnson had promised a "cautious but irreversible" route out of lockdown, but on Monday said the Government would take "whatever steps necessary to protect the public".

One undated paper warns that "it is highly likely that transmission will increase in autumn and winter". It says: "The healthcare burden of other infections through the year is also an important consideration. This may mean stronger measures may be desirable for autumn and winter."

On Monday, Mr Johnson said cases may reach 50,000 a day by July 19, with his chief scientific adviser, Sir Patrick Vallance, warning that case were doubling every nine days and now stood at more than 27,000.

The Sage documents say that "there is significant risk in allowing prevalence to rise, even if hospitalisations and deaths are kept low by vaccination. If it were necessary to reduce prevalence to low levels again … then restrictive measures would be required for much longer".  

The documents make a detailed case for retaining measures such as face coverings. Minutes of one meeting on April 22, which were only released on Monday night, say: "Ongoing baseline measures and sustained long-term behavioural change will be required to control a resurgence in infections."

Keeping such measures could cut transmission by as much as a quarter, the minutes suggest, warning that "lifting restrictions may re-create the conditions for ‘superspreader’ events". It says these could be "both person-driven (one highly infectious but possibly asymptomatic person going to multiple places) and setting-driven (nightclubs, religious events where crowding is experienced, low ventilation, loud activities etc)."

A paper drawn up by subgroup the Scientific Pandemic Insights Group on Behaviours a week later says: "Sage has concluded that, as legal restrictions are eased, maintaining low levels of transmission will require continuing policies that promote Covid-protective behaviours."

An undated paper considering which measures are likely to be needed "beyond the end of the roadmap" includes a section on "the need for ongoing measures".

It says these would "significantly decrease ongoing transmission" and adds it is "notable" that countries such as New Zealand that have near-zero Covid retained measures such as the wearing of masks on public transport.

Sir Patrick told the Downing Street conference: "We are in the face of an increasing epidemic at the moment, and therefore we need to behave accordingly." 

Prof Chris Whitty, the chief medical officer, said there was a "pretty high degree of scientific agreement" that the delay of four weeks before moving to stage four of lifting lockdown was a good idea. 

Covid rules from July 19

But he said the view about the right time to relax restrictions was "more mixed", adding: "There is quite a strong view by many people, including myself actually, that going in the summer has some advantages, all other things being equal, to opening up into the autumn when schools are going back and when we’re heading into the winter period when the NHS tends to be under greatest pressure for many other reasons."

Under the changes, mask-wearing will no longer be legally required except in some settings such as medical environments. 

On Monday, Mr Johnson, Prof Whitty  and Sir Patrick were asked when they personally would continue to wear masks. 

Mr Johnson said the Government was trying to move from a "ditktat" to relying on personal responsibility, saying: "There’s a big difference between travelling on a crowded Tube train and sitting, late at night, in a virtually empty carriage on the main railway line."

Prof Whitty was more specific, saying he would wear a face covering in crowded indoor situations, when required to by an authority and if someone else was uncomfortable, as a "point of common courtesy" – a view echoed by Sir Patrick.