The point is that it's absolutely irrelevant if the lockdown was loosened or tightened, if UK entered tier 4, 5 or 127. The indisputable fact is that millions of people travelled on Christmas day to visit friends and families, allowing the virus to spread. For a large number of those, such a visit was simply not possible just a day before because they were already in Tier 3 where meeting people inside was not allowed. So yes, Christmas day was a significant "loosening" of restrictions for those people.