Hi Ali!
Your interview is a day before mine! GOOD LUCK!
Now, I might be wrong, but I'm pretty sure that these positions are for LHR. That's what it said on the website anyway...The vacancies were for FA's based in LHR. I'm not sure if it's for SH or LH, or when we will get told, but I'd assume it would be for SH, and I also assume we will get told when they offer you a position, which I was told by BA HR, is 5 days after the interview.
Sorry I couldn't give you any definate answers!