I take your point but on the other hand do we as a country recognise maybe Christmas is celebrated in ways it wasn't over 50 years ago?
How do you mean "on the other hand"? I don't understand how that's the other hand to what I was saying.
Taking your 50 year timespan, almost nobody in any British workplace right now was attending any workplace Christmas parties before that. The vast majority of publicly-visible Christmas celebrations have been barely identifiable as linked to anything Christian for longer than most people can remember. Unless you choose to go to church services, it's what, the school Nativity play and Carols from Kings?
As for the rest of it, almost anyone can and does take part to a greater or lesser extent. I've never been Christian, but woke up on Christmas morning to presents from Father Christmas, eat a big roast every year, and go to Christmas parties. If I lived somewhere else, I might do different big meals and parties and gift-giving.
I suspect that in most ways, things were much the same fifty years ago, and are much the same in other many countries where there might be a stronger religious link to the big, cohesion-promoting public holidays — people who don't do the religious part or share some of the practices still like to join in with the culturally-sanctioned time of carnival/chaos/community/general celebration.
Okay, if "Christmas party" was at some point (or still is) a universal code for "everyone get pissed as fast as possible with a load of random people you didn't choose to spend your days with" then no, people with cultural or religious taboos about alcohol won't be able or willing to participate, I suppose, but then it doesn't really matter what you call it, it's still grim as fuck.
I was just trying to get you to imagine how it might feel to be on the other side of your question (in 2023).