UK Prime Minister Boris Johnson has said he does not want Britons to cancel their Christmas parties or Nativity plays as he announced plans to tackle a rise in the cases of the Omicron variant.

The prime minister said on Tuesday during a No 10 Downing Street press conference on the variant that another lockdown was "unlikely." But the government will keep "everything under review" and plans to expand the booster vaccine rollout, he said.

He vowed to offer everyone eligible a COVID booster jab by the end of January.

Johnson has promised to "throw everything" at the vaccination drive over the next two months amid fears of the new Omicron variant.

Older people and those considered vulnerable will be given priority in the new program, with the NHS going down age groups in five-year bands.

(With input from agencies)