I made an OCI application for me and my father in Birmingham, in person, on 25th January. The thing is, I changed my surname, and my dad has also changed his first name (don't ask!) so the woman at the counter got a little confused and said my father might need an interview. (It's all genuine though...

I don't think it should be an issue. It's probably something they'll overlook, unless they're looking for reasons to refuse!