I was invited in to a group interview (as the store was opening soon) and they collected us all from outside and led us to the interview room. They had a quick ice-breaker where they made us introduce the person they paired us with. Then they asked us some fairly generic questions about customer service and asked us to fill out some forms about availability and which stores we'd be happy to work at etc. etc. After that they were in contact within a week to invite me to an induction day (paid) in central London where they assigned us our stores and roles as well as giving us more information about the company.