I applied through a staffing agency. The process took 4 months. I interviewed at Brook Street (Derry, Northern Ireland) in Jan 2015
Interview
Assessment day took ages to receive answers after event prior to assessment day registered with manager of branch who was extremely nice and professional and extremely accommodating. Interview had to be rescheduled for poor weather and lasted 2 hours though security process could spend up my application because I had prior clearance took longer than ever.