I applied for Sheffield depot recently, they're on a big recruitment drive. I passed the assessment day and am now just waiting on medical & start date.
Things are moving very quickly and it doesn't look like people are just going to be put in a talent pool. The interview itself digs into your customer service experience and work experience, if you have plenty of this then you'll be fine, just be ready and be prepared to go into the archive of your working life and pick out your best examples. Aside from this, standard interview questions are involved, if your motives for applying fit then you'll have no problem answering these.
Good luck to anyone applying, the impression I got of the company on the assessment day made me want the job more, the managers and interviewers were great and very personable and gave it a real family feel. Just be prepared!