The reason I moved to derived classes was for maintenance , if I add another member to my interface I obviously have to implement it in all my classes ( which is what I've reverted to anyway because of the empty objects ) , I don't totally understand why the derived class method resulted in null values, the structure I had in mind ( which didn't work ) was, to define an interface,implement the interface in a base class, create subclasses of the base class, the reason I need subclasses is I decorate the properties I require for my CSV serialiser with a custom attribute which allows me to sort the order they are serialised and include or exclude them from the output. What I find inconsistent with interfaces ( and I love them ) is if you subclass a base class that implements an interface you don't have to implement the interface in your subclass - which is why I went that route but ended up with empty objects, in one of my methods for adding an object to a list for testing purposes instead of using new T() I typed my class instance ( I was using a derived class at this time )

Tariff1 t = new Tariff1();
t.SomeProperty = "Viv";
t.OtherProperty = "Greg;
this.Data.Add(t);

Now this is what is confusing me, if you inspect "t" it has "Viv" and "Greg" as values, Data[0] doesn't