I applied online. The process took 3 weeks. I interviewed at BAE Systems in Mar 2015
Interview
1) Fill out an online application form
2) Wait for an email off HR saying whether or not you have got an interview
3) Go to the "assessment centre" where you'll do three activities
a) Interview - Fairly relaxed but of a formal nature
b) Group Exercise - Groups of 5/6, given a scenario and a big list of options. As a group, decide which 5 options out of the whole list you should pick and why
c) Presentation - In the "interview" email, you'll be asked to create a presentation in preparation for the assessment centre. You'll then present this in front of assessors (it was 2 assessors for me).
4) Wait for another email saying whether or not you've been successful