Your application and CV is only reviewed by HR once you pass the online tests, which are used to weed out the weaker people. HR are very kind, and will help you to arrange any transportation or overnight accommodation at the assessment centre. There will be about 15 candidates at the assessment centre, all of them applying to the same business area. The intern, summer intern, and graduate applications spend the day together in the same group. The majority of the other people are from top-ten universities like Oxford and Cambridge, with lots of prior industrial experience, so the competition is high! You have to redo the numerical test, which has the same format at the online test you have already done, but will be completed on paper instead. There have been stories where people have done well at the assessment centre and were seriously considered for an offer, but only to have failed the numerical test. You then have to give a 10-minute presentation where you are given the opportunity to pitch yourself. This is followed by a competency interview, where they will ask the standard questions ("give an example of a time when you...?"). I would recommend researching as much as you can about the company beforehand. (protip: make a note of the current share price!) You are then split into teams of 5 for the group assessment. You are given about 45 minutes to complete a set task, which will usually consist of an element of design, costing, and construction, etc. Finally you have the technical interview. This is (in my opinion) the hardest part of the assessment centre. You will be asked a whole range of questions relating to the business area you have applied to. This may include showing you some graph or technical data and asking you to explain it. They don't expect you to know all of the answers, but instead are trying to see how you think and approach the problems. They will also show you a component from a jet engine, and will ask you every possible thing about it, ranging from the function to the manufacturing processes and materials used. HR will contact you within the couple of days you to let you know of the outcome of the assessment. Good luck!

Interview went very smoothly. They know its stressful so they tell you that they are okay with you taking a moment to gather your thoughts. They mostly just ask very general behavioral questions. I had two 30 minute phone interviews which were almost identical, one with a recruiter and one with a hiring manager.