Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 31 Maundy Thursday
April 01 Good Friday
April 03 Easter
April 04 Easter Monday
April 25 General Prayer Day
May 12 Feast of the Ascension
May 18 Pentecost
May 23 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions