Welcome to the Cake Decorators Q&A

i am also interested in Mrs Jones use of self raising flour rather than plain flour and a raising agent

You can use plain or self raising. SR has the raising agents already included for convenience, at one time only plain flour was available so raising agents had to be added. I think it all comes to down to personal preference and what the recipe asks for. You will also notice some recipes ask for baking soda when liquids like sour cream or butter milk is used. Because baking soda reacts with moisture and starts to work straight away forming carbon dioxide bubbles, batter containing BS should be baked straight away to insure a well risen cake. There are also different grades of flour depending on the kind of sponge being baked and, specialty flours for specific dietary needs. Super fine flours are available for baking extra light whisked sponges and certain biscuits such as Viennese fingers. These are labeled as 00 grade.