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"?
The cherry cake in More Fast Cakes (1985) has 175g SR flour and 1tsp baking powder, and the "English cherry cake" in Mary Berry's Ultimate Cake Book (1994 reprinted 2003) has 275g and 2tsp. Recipes with both aren't unknown but this seems like a lot of extra baking powder. It must be meant to rise a lot
Apart from children's books most of the cakes I make are from her recipes and they seems reliable.
I assume you used the deep cake tin specified. I can't instantly lay my hands on mine but it's about 4" deep.
How accurate is your oven temperature? A recipe like this would rise fast, and may be prone to over rising then dropping if cooked too fast. The later recipe cooks rather cool at 160C/325F,and that's without a fan.