Geoff Barton, General Secretary of the Association of School and College Leaders, told Sky News that the rising number of teacher shortages could also mean supply teachers are not given enough time to be drafted in to cover those off sick, forcing schools to shut. It comes as another teaching union head warned that half of all teachers could be isolating by Tuesday.

       Mr Barton explained how a primary issue is the notice period given to supply teachers to fill in for those COVID-19 sricken teachers forced to self-isolate.

       He said: “The difficulty with the people I represent as school and college leaders is they won’t know until Tuesday morning, 8 o’clock…

       “When they start to get phones calls as to how many staff have tested positive and therefore will not be coming into school.”

       He added: “It is not like we have got lines around the block of supply teachers who can suddenly at the last minute step in and do that.”

       JUST IN ‘I don’t accept that!’ BBC Breakfast’s Luxmy Gopal blasted by Robert Halfon in mask debate

       He stressed how the issue of supply teachers "is the biggest risk... to us having no disruption”.

       It comes as Prime Minister Boris Johnson said he was "absolutely determined" to keep schools open in January despite record numbers of COVID-19 infections over the Christmas period.

       While Paul Whiteman, General Secretary of the National Association of Head Teachers said "half" of teachers could be off work by Tuesday.

       He welcomed the Government’s plan to keep schools from closing but stressed getting resources into schools to prepare for high numbers staff absences was vital.

       READ MORE When are we going back to school? Are Year 12s going back? Full school return guide

       He told Sky News: “Everybody understands that keeping in school is the best thing to do, so that has to remain the focus.”

       Most kids will be back at school by January 10.

       Despite Mr Johnson's demands to keep schools open, scientists have warned that more than 1 million kids could be at risk of catching the virus.

       It comes as Dr Mary Bousted, joint general secretary of the National Education Union, blasted the Prime Minister and the Government for delaying the now in-force optional mask wearing in schools, saying action is "overdue".

       DON'T MISS

       Surgeon admits 'we don't want to stop Omicron spread' across UK [INSIGHT]

       Tony Blair gets knighthood from Queen in NY honours list [NEWS]

       New rules from TODAY threaten to wreak havoc on UK [EXPLAINED]

       The Government have also sent out 7,000 air-cleaning units for classrooms to stay ahead of the virus.

       She also told The Mirror: “ “The fact the Government has provided the extra purifiers shows it recognises the problem but with over 300,000 classrooms in England they have failed to provide an effective solution. Finally, the Government have been forced to recognise, and react to, the scale of the Omicron variant and its potential impact on education."

       Health Secretary Sajid Javid has also casted off concerns of further Coronavirus restrictions, saying new measures are an “absolute last resort”.

       He said: “Curbs on our freedom must be an absolute last resort and the British people rightly expect us to do everything in our power to avert them."

       In England a record 162,572 Covid cases were registered in the latest 24-hour period, Government figures show. The UK has now recorded a cumulative 246,780 cases of the Omicron variant.