Despite the world's current climate, BA as far as I know were still recruiting SSPs for the Airbus. There are a few more CTC students in the company now which is good to see as it was always generally Oxford SSPs who went through the system with BA. However, more CTC students are being put forward now. You do start on an SSP scale but this rapidly increases and continues to increase year on year. Once you start flying you can expect an extra £1200 a month allowances. I'd say it's simply the first 3-4 months you really have to plan carefully for when it comes to money. After 4-5 years the world is your oyster and you will probably have the option to bid to move onto the 747, 777 or A380.
With regards to the part time work idea I think as the holder of a student visa you're allowed to work 15 hours a week. Personally I think it's pretty foolish to comprimise the quality of your education in NZ for the sakes of a bit more spending money in NZ. Part time work in NZ comes in at around £4 an hour as that's the minimum wage out there. I'd say take the extra dough from HSBC and just accept you'll be paying a few extra pounds a month once you start paying back your loan.