Sajid Javid said: "I'd say this, if you are asking me for guarantees, I will just say - as the Health Secretary, of course, I'm not the Education Secretary - that there are, when it comes to our fight against this pandemic, there are no guarantees. But what we do know works is, in this case, a booster shot of the vaccine."

       His warning comes after Education Secretary Nadhim Zahawi said on Sunday that he could not guarantee that in January all schools will be open.

       Paul Whiteman, general secretary of school leaders' union NAHT, says there was already "chaos" in some schools following the emergence of Omicron.