Here in British Columbia we have a 'household only' order in place since Dec 15, so we all knew in advance not to plan visitors or extended family for Christmas dinner. The exception is for single people - they may go to one household where they are already in regular contact.
It will be just myself and my husband. He will go to the hospital to visit his mother in the morning, and we will facetime or phone our grown children and families.
Boxing Day if the weather permits I may ask to go for a walk with them, which is allowed.
I feel badly for those in Britain that had plans and now need to cancel, but understand the need.
Also I would like to say that Christmas is not cancelled. Celebrating with any other than household is. We can all celebrate in our own small way. Santa is still expected to visit children at night, we can watch Christmas mass on livestream if you check your church plans; we can eat a nice meal and watch Christmas movies, play board games and listen to Christmas music. Reflect on how little we actually need, and how much we actually have, and value the connections we have to friends and family.