Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 19 Maundy Thursday
March 20 Good Friday
March 22 Easter
March 23 Easter Monday
April 17 General Prayer Day
April 30 Feast of the Ascension
May 10 Pentecost
May 11 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions