Interviews at TfL are all competency based with up to 4 questions on competencies appropriate to the role. The mark scheme is incredible prescriptive. There is usually also a technical question with interviews taking around 1.5 hours for middle management roles. Preparing for interview is critical as if you don't say the exact right thing you won't get the role. The interview itself isn't hard per se, but meeting the required standard based on the incredibly narrow marking scheme used, is difficult. Even those internally who are already doing similar roles and responsibilities struggle to secure roles. There is no direct promotion though so if you are coming into the company from outside or moving to another type of role internally then there are more opportunities available, which is maybe a positive for some.