I applied there about a year ago and completely blew the final interview - there were quite a few 'tests'
Firstly there was an online maths test - was fairly basic stuff (I think the time you take to complete it was recorded though)
next stage was at their offices for two paper based tests - one was a basic maths one (though under some time pressure) and the second was again fairly basic questions but involved some data - say sets of 4-5 questions etc.. relating to a chart/table/graph etc...
the next trip to the office involved an IQ type test - fairly standard tbh.. involved the usual stuff sequences, shapes etc... was also given some form of multiple choice management training type test where you rate your answers in terms of strongly approve/disapprove
was also an interview with one of their managers and some mental arithmetic questions
next stage involved another test (they do seem to like tests!) was some card based game that involved finding patterns etc..
final stage is/was an interview with one/two of their traders
of course all this may well have changed by now