...plain teacake (so distinguished from just a "teacake" which,as your friend discovered, can mean the fruit variety) or cob (which can sometimes mean a round loaf about 9" across)

Not in Yorkshore or the West Riding as was, anyway). A "teacake" would automatically be plain bread. If you wanted the fruit variety you'd have to ask for a "currant teacake".

And then there was the "long bun"...a longer, thinner version of the currant teacake.