Are the terms self-rising flour and baking powder different in the US and UK?
The answer to your question is nope. The UK and USA are in agreement on this one. Self-rising flour and baking powder are the same on both sides of the pond. See also Translating cooking terms between US / UK / AU / CA / NZ

Note: I thought that two tsp of baking powder was an odd thing to see in a recipe that uses self-rising flour so I looked up a Mary Berry cherry cake recipe. The BBC published a recipe on their website and it doesn't call for baking powder. Are you sure your recipe didn't say "OR"?