Your Dad is correct that Baking Soda is bicarbonate of soda, aka sodium bicarbonate, but you can not just indiscriminately switch it for Baking Powder, or use Baking Powder in place of Baking Soda. Read this explanation
of what they are and then read this information on substituting
one for the other (there is also info on substituting flours and other baking ingredients).
What you end up with depends on all of the ingredients (fat, sugar, acid, leavening agent, flour, liquid, temperature, method, etc.). Here are three recipes for chocolate chip cookies that will demonstrate how alterations to the recipe will give you 3 totally different results (compare the ingredients and the method of combining them) Thin
(most people will instantly recognize these as the recipes from Alton Brown's episode Three Chips for Sister Marsha
) - there is also a good indepth discussion of these three recipes in Shirley Corriher's book, Cookwise
You can also find some good information on cookies and ingredients on the cookie pages
at Baking911. There is a good section on basic "TIPS" that explain a lot is you should really read that section. There is also a "what went wrong?" section with how to correct your recipe.
One more thing about flours - if I remember correctly, in the UK what is called "plain" flour is what we in the US call "all-purpose" flour, and what they call "white" flour in the UK is what we call "self-rising" flour in the US - it comes with baking powder already mixrd into it, so if you were using it in place of plain flour you would have to eliminate the leavener called for in the recipe (and if the recipe called for baking soda you would have to make the adjustments for changing from soda to powder).
As for the scones - don't know what you changed in the recipe ... there is a good chance that you did make scones.