The Prime Minister is to set out the basis of plans for the festive period on Monday, as well as detailing a new tougher three-tier system for England when its national lockdown ends on December 2.
But Mr Johnson will be unable to say how many households will be allowed to mix over Christmas and for how many days restrictions will be relaxed for until a later date, the PA news agency understands.
Cabinet Office minister Michael Gove met with leaders of the devolved administrations over the weekend to agree “a shared objective of facilitating some limited additional household bubbling for a small number of days”.
But the public will be “advised to remain cautious” and told that “wherever possible people should avoid travelling and minimise social contact”, a statement from his department said.
Mr Johnson will still detail the strengthened tiered system in a statement to the House of Commons on Monday, but the full details of the festive relaxation is not expected until after the first ministers of Scotland, Wales and Northern Ireland consult their own cabinets.