Britain's biggest teachers' union has backed a "circuit-breaker" lockdown and called for secondary schools and colleges to be closed for an extended two-week half-term.
The intervention by the National Education Union (NEU) comes amid sustained pressure on Boris Johnson from Labour, Government scientific advisers and the NHS for the reintroduction of draconian nationwide restrictions.
Speaking at a press conference on Friday, the Prime Minister said he wanted to avoid such measures, but "cannot rule anything out".
Earlier in the pandemic, the NEU came under fire for resisting attempts to get children back into classrooms before the summer holidays despite the devastating effect of school closures on pupils' learning.
Although coronavirus poses almost no risk to children, schools were closed from March 20 and most only reopened in September.
Earlier this year, the Government's Scientific Advisory Group for Emergencies (Sage) warned that the damage to children caused by missing out on school would last a lifetime.
Disadvantaged pupils have been the most adversely affected, and Michael Gove admitted in May that the progress in closing the gap between the richest and poorest had been put back by lockdown.
An extended half-term would also present problems for parents who would have to once again grapple with childcare on top of work.
While any "circuit-breaker" may be described as a temporary measure, reopening schools again if cases did not fall could prove difficult.
Kevin Courtney, the joint general secretary of the NEU, said teachers understood the adverse impact that closing schools for an extra week would have on children's education but added: "We also understand that, in exponential epidemics, early action is essential.
"Taking action now can avoid more disruption later. The Government must not just turn a blind eye and pretend all is going to be OK."
Earlier this year, Mr Courtney told the union's 450,000 members not to "engage" with the Government's plans to reopen primary schools following the May half-term.
The NEU's calls for children to stay at home for an extended half term break put it at odds with ministers, who are keen for schools to remain open even in parts of the country deemed to be "very high" risk.
Covid infection rates are rising more sharply among secondary school pupils than any other section of the population apart from university students, according to the latest data from the Office for National Statistics (ONS).
Over a three-week period, the proportion of pupils aged 11 to 16 testing positive for the virus more than almost doubled, from 0.28 per cent to 0.93 per cent.
This growth is second only to those aged 16 to 24, where the proportion testing positive rose from 0.5 per cent to 1.49 per cent over the same period of time.
The vast majority of schools in England have a one week half-term holiday during October, most of which take place during the final week of the month.
Schools in England must open for a minimum of 190 days during the academic year, but it is up to individual local authorities and governing bodies to set term dates. That means headteachers could order a two-week half-term break with or without the Government's permission as long as the days are made up elsewhere in the school year.
The NEU's intervention comes amid tension between the Government and its scientific advisers over how best to control the second wave of coronavirus.
On Monday, Sage minutes revealed that the body had called for a "circuit-breaker" lockdown three weeks ago. It also emerged earlier this week that Government scientific advisers had said "circuit-breakers" should be planned for every school holiday.
On Friday, the Government's chief scientific adviser, Sir Patrick Vallance, suggested "extra measures" would be needed on top of those required in the highest tier of restrictions. He told a Downing Street press conference: "Tier 3 baseline conditions on their own almost certainly aren't enough to get the 'R' below one".
A "circuit-breaker" has been called for by Sir Keir Starmer, the Labour leader, and Andy Burnham, the Mayor of Greater Manchester, who is demanding the national measure in his row with the Government over whether the region should face tougher restrictions. It has also been backed by NHS Providers, which represents NHS Trust leaders.
Mr Johnson told the Downing Street press conference: "Some have argued that we should introduce a national lockdown instead of targeted local action, and I disagree. Closing businesses in Cornwall, where transmission is low, will not cut transmission in Manchester.
"So while I can't rule anything out, if at all possible I want to avoid another national lockdown, with the damaging health, economic and social effects it would have."
A Government spokesman said: "Schools have put in a range of protective measures, endorsed by Public Health England, to reduce the risk of transmission.
"The chief and deputy chief medical officers have repeatedly confirmed that children do not drive infections in the community in the same way as with other infections like flu.
"Their assessment remains that the risks to children's education and well-being from not attending school outweighs any other risks. Any decision to restrict school openings would be made only as a last resort."