Are the terms self-rising flour and baking powder different in the US and UK? I made Mary Berry’s Cherry cake, which called for 275 g of self-rising flour and 2 tsp of baking powder, in an 8-inch pan. Went all over the oven. Are these ingredients different in the US?
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"?