Boris Johnson has failed to guarantee that schools in England will reopen on time next month, after minsters warned a new strain of the coronavirus pandemic was out of control.
Teaching unions have called for the return of schools to be delayed after it emerged that the mutation is highly contagious.
At the weekend the health secretary Matt Hancock said he could not rule out school closures of the kind seen during the first lockdown in March as the government battles the threat.
The Northern Ireland health minister has already suggested that schools there are unlikely to reopen as expected after the Christmas holidays.
The new variant forced the prime minister to cancel the Christmas plans of millions on Saturday.
At a press conference in Downing Street, Mr Johnson said he wanted to stick to the current plan of a staggered start for schools in January “if we possibly can”.
He added that the common sense thing to do was to “follow the path of the epidemic”.