I applied online. After telephone interview I was invited to assessment center. I attended the assessment center in London. Nice office, quite spacious. Their were two interviewer, but only one interview depends on your preference. Then a serial of tests, including technical, aptitude, maths and some general knowledge (some of the questions are more like brain teasers). Nothing difficult except for technical type questions that I think I did not do well. I do not think the tests are the problem, the problem is the interview with account manager, who will probably be your manager in the future. So give them good impression and if they like you, you have great chance to get the offer.