Assessment centre lasts a full day from 9-3/4pm, theres technical question, customer service questions, group based work, presentation and then overall questions at the very end about how you think you did.

Assessment centre comprised of 4 activities. Scenario based interview, individual presentation, group presentation and self reflection chat. A half day was spent there. They were very welcoming. They brief you about the activities on that day. You just need to do a little research on the company, the role you are applying for and your motivations for working at BT