Applied online, a few months later received a call wanting to do a phone interview. It was pretty simple and easy going. I was then instantly invited to the assessment center in Birmingham. The assessment centre was done in two parts: morning and afternoon.
The morning consists of 4 tasks: an IQ test, written test, group presentation and a team work exercise. Once these have been completed you have lunch and await their decision about whether you will continue to the afternoon stage. If they don't want you, you leave early. I think the afternoon stage was just an interview with a member of staff.
The actual centre was in Birmingham and I found it enjoyable despite not making it to the afternoon stage.