I want to just add on say that Milbank's WG is a stage 2 assessment.Other firms with Watson Glaser/Critical Thinking Test (Apps still open):
Milbank
Cooley
Cleary Gottlieb
Addleshaw Goddard
I've made a list for Amberjack before on this thread, worth check it out.
Other firms use Cappfin and SHL (Ashurst, Osborne Clarke, etc). The rest are quite direct either with written exercise or interview.
There is an SJT and timed application questions for stage 1!!