Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 19 Maundy Thursday
April 20 Good Friday
April 22 Easter
April 23 Easter Monday
May 18 General Prayer Day
May 31 Feast of the Ascension
June 10 Pentecost
June 11 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)