This sponge cake probably was a Victoria Sponge cake. It is a 'sandwiched' cake with jam, buttercream, or whipped cream +/- strawberries in the middle. It is truly delicious. The WI would say that jam in the middle is the 'correct' version. Self raising flour is flour with a raising agent added by the manufacturer. Flour for baking, in the UK, is either plain (probably your all-purpose flour), and self raising. There is also bread making, pasta, gram, spelt, buckwheat and other types of flour available here. I am attaching a link for the WI Victoria sponge, but of course, it may have been a different type of cake your friend was thinking about.
https://www.thewi.org.uk/what-we-do/...toria-sandwich