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.

Rules kept getting stricter on paper but none were really enforced in the real world

it was made it more strict on Christmas Eve.

What matters is if people follow lockdowns. Are people getting fatigued? Starting to resist where before they complied?