Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 04 Maundy Thursday
April 05 Good Friday
April 07 Easter
April 08 Easter Monday
May 03 General Prayer Day
May 16 Feast of the Ascension
May 26 Pentecost
May 27 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)