Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 15 Maundy Thursday
April 16 Good Friday
April 18 Easter
April 19 Easter Monday
May 14 General Prayer Day
May 27 Feast of the Ascension
June 06 Pentecost
June 07 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)