I applied online. The process took 4 months. I interviewed at Mace (London, England) in Apr 2018
Interview
After an online application form, got invited to interview. This was with two people, and was informal and more of a chat with the occasional sneaky interview question slid in there, but in a conversational way. Was mostly questions centered on the past experience I mentioned in the online form, asking me to go into more detail.
Got invited to assessment center that was two months later. Despite there being a dozen people there, only a handful were in direct competition with me. Getting to the assessment center meant I had a 50% chance of getting the job already (at least in my case). It involved no second interview, and no online tests. Only required two group exercises both of which where we would all work together on a project very related to the job itself and they were looking for teamwork and not leadership. The final assessment was a individual exercise, where I was given an hour to make a 10 minute role-play style presentation. It was only to one assessor, and I personally was allowed to sit down to deliver it because I was nervous.