There was an online application which included situational questions. After I passed that they rang me to invite me to a group interview (which they call a 'Magic session').
In this session there were 16 on us. We were paired up with the person next to us and had to ask them general questions about them then introduce them to the rest of the group. After that we watched an Asda promotional video about how good it is working there, then had a do-it-yourself part where we basically went in-store and rearranged stock like a normal employee would. When we returned we got split into two groups and had to make a structure out of marshmallows and spaghetti, which one person from the team had to pitch to everyone else. It wasn't very serious at all and it's more to find out about your personality and teamwork skills.
I passed that and got called to an individual one-to-one interview. Questions inlcuded previous examples of teamwork, good customer service, ability to work alone and use inituitive, what you'd do with an uncooperative team member etc. She also asked about my hours and flexibility, which was also a part of the group session. The interviewer was nice. A few days later I got an email saying I didn't get the job. Other people who did get the job got a phone call.