Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 08 Maundy Thursday
April 09 Good Friday
April 11 Easter
April 12 Easter Monday
May 07 General Prayer Day
May 20 Feast of the Ascension
May 30 Pentecost
May 31 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)