I have to say I am increasingly of the opinion that the Christmas Bubble should be abandoned.
Firstly, as others have noted, there is absolutely nothing special about December 23rd - 27th. It sends completely the wrong message that it can be so dangerous that you can't visit a restaurant on December 22nd and 28th but in between those dates everything is fine.
Secondly, as this goes for the tier system more generally, is that is will cause people to act more recklessly than if we had a simpler, more sustainable, set of rules. Tell people that they have "5 days off for good behaviour" before being locked inside again for who knows how many months to come and people will take it (and then those in charge will act shocked when they do) For examples of that just look at what happened before Lockdown 2 and in the run-up to entering tier 3 - People see a final chance to do stuff and take it.
It is a terrible decision to have to make...but if the alternative is lockdown 3 in January I know what decision I would take.