Naughty Girl
The GB interview is very relaxed - there are no wacky psychometric tests or technical questionaires. There will be a company presentation by them, a brief group exercise and an interview. The interview is usually conducted by a senior captain and a human resources lady. It is very straightforward with no awkward questions. Stuff like - "Tell me about an tricky situation you have had with a captain" is about the hardest. There is also a buffet lunch where you stand around and talk with the pilots that are doing the interviews - this actually forms part of the assessment so you should avoid saying anything stupid! If you are successful they will phone you within 24 hours and invite you to a sim ride on the 737 - even though they are an Airbus company and you may be Airbus-rated.
My best advice is just to be yourself - they are delightful people and know exactly who they want so do not try and be something you are not. Best of luck.