Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 16 Maundy Thursday
April 17 Good Friday
April 19 Easter
April 20 Easter Monday
May 15 General Prayer Day
May 28 Feast of the Ascension
June 07 Pentecost
June 08 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)