Wishing you a very Happy Christmas from Hankins English.
In the UK Christmas day is a national holiday (祝日) and so most people have the day off.
Generally speaking British people spend Christmas with their families like new year in Japan.
In the morning we usually open our gifts.
Gifts from Santa (in the UK Santa is also called Father Christmas) are sometimes put in a Christmas stocking (クリスマスの長靴下), but families often put presents under a Christmas tree too. In the UK, adults also receive gifts and children get some presents from relatives and friends, so there are often many gifts to display. A lot of families get a real tree from special tree farms.
As Christmas day is a holiday, most people have a special lunch together, not dinner like in Japan. It is usually a very big meal with some kind of roast meat (usually turkey or chicken but sometimes ham or beef) with vegetables and other side dishes. The traditional desert in the UK is a Christmas pudding.
The day after Christmas (December 26th) is also a national holiday in the UK. It is called Boxing Day, because in the old days people used to give servants and poor people (使用人や貧しい人たち) gifts (a Christmas box) on this day. You can read more about Boxing Day here: https://ja.wikipedia.org/wiki/ボクシング・デー