I’ve googled it for you
.Celebrations with official, nationwide status across the UK are generally limited to bank holidays and royal events, including
Christmas, Boxing Day, New Year’s Day, Good Friday, Easter Monday, and the Early/Late May/August Bank Holidays. Other officially recognised events include the monarch’s official birthday (June) and national occasions like Remembrance Sunday.
Key Regional National Days (Not Official Public Holidays Everywhere)
St David’s Day (Wales - March 1st): Widely celebrated but not a statutory bank holiday.
St Patrick’s Day (Northern Ireland - March 17th): A public holiday in Northern Ireland.
St George’s Day (England - April 23rd): Not a public holiday.
St Andrew’s Day (Scotland - November 30th): A bank holiday in Scotland.
So generally Christian based customs / celebrations because the country is officially Church of England