Schools should not be closing early for Christmas unless they have been told it is “necessary” on public health grounds, Downing Street has said.

The Prime Minister’s official spokesman indicated that schools would be kept open unless there is an “absolute public health emergency”.

Local authorities have been warned against shutting schools early for the festive break simply as a precautionary measure.

Asked whether schools might close early for Christmas, the Prime Minister’s official spokesman said: “Certainly we do not think anyone should be closing schools early unless they have received advice from the local director of public health that it’s necessary on public health grounds.

“We wouldn’t want to see that happening routinely, just as a precaution, because as I’ve said, education is vital. And we’ve seen, sadly, because of the public health crisis, children have to miss face-to-face education. And so it’s very important that we maintain schooling as much as possible.”

It comes after a teaching union urged the Government to stagger the return of pupils to schools in January amid concerns about the Omicron variant.

Meanwhile, a heads’ union has warned that delaying action until vaccination can take hold could keep children away from class “longer” in the long term.

The NASUWT teaching union is calling on Education Secretary Nadhim Zahawi to urgently announce additional measures for schools and colleges before the Christmas break to avoid a repeat of the “chaos” last year.

The Government should publish guidance advising schools to cancel or postpone non-essential activities and events immediately, as well as move to online staff and parental meetings, the union says.

It adds that a staggered return of pupils in January should be considered and extra on-site testing facilities should be provided until the February half-term.

Health Secretary Sajid Javid said he could not guarantee schools would not close again due to the pandemic.

It comes after Mr Zahawi said on Sunday he could not guarantee that in January all schools would be open everywhere.

In Wales, two councils, Denbighshire and Anglesey, have decided to end face-to-face classes early on Friday December 17, with students expected to learn from home for the last three days of term.

In a letter to the Education Secretary about the Omicron variant, Dr Patrick Roach, general secretary of the NASUWT, said: “I must urge you now to consider the immediate introduction of additional education measures to help slow the spread of Covid-19 and to minimise further disruption to education.

“In addition to wider community-level measures, we believe that additional measures will be required within schools and colleges now and as they return after the Christmas break.”

Dr Roach added: “We ask you to avoid a repeat of the confusion and chaos which last year impacted negatively on public and parental confidence and hampered the hard work of teachers and school and college leaders in their preparations at the start of 2021.

“An immediate announcement from the Government on additional measures for schools and colleges is, we believe, essential before the majority of schools and colleges close for the Christmas break.”

After the Christmas holidays last year, Prime Minister Boris Johnson told parents on January 3 to send their primary-age children back to school.

But on the evening of the next day, he announced a national lockdown for England – with all schools closed to the majority of pupils.

Robert Halfon, Conservative chairman of the Education Select Committee, has said the Government needs to “make sure schools are kept open in January”.

Mr Javid told MPs on Monday: “One of the reasons to take the measures we’ve said, especially around expanding the booster programme, is to make sure we can prioritise our children.”

The NASUWT is also calling on the Department for Education (DfE) to publish the levels of teacher and support staff absences – both Covid and non-Covid related – and the steps being taken to ensure schools can continue to maintain quality education provision amid “serious” staffing shortages.

Dr Roach added that figures reported to the union suggest that between one-third to one-half of teachers at  some schools are “unavailable to work.”

Mr Whiteman, general secretary of the NAHT school leaders’ union, said: “It is already chaos in some schools as the Omicron wave hits.

“Delaying action until vaccination can take hold may actually keep children away from school longer in the long term.

“We would urge the Government to take every safety measure possible while maintaining face-to-face education, in order to avoid longer term school closures.

“Infection rates in schools have been growing unabated for a long time. Simply relying on the fact that children tend to suffer less from the virus is not good enough.”

He added that the Government “must act now” to deliver ventilation solutions and “sensible and effective” isolation protocols.

Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said: “What we may see is schools periodically having to close or send home year groups, for short periods of time, because of unsustainable levels of staff and pupil absence, or on public health advice.

“This has already been happening during the course of this term and there could be more of this if the Omicron variant means that there is more disruption.”