CV and cover letter, a written test and then two assessment days. I made it through the first but declined to attend the second. The second required you to create a presentation from a list of topics they give you, and other interviews.
The assessment day was very long and involved a lot of waiting around and listening to presentations, without very much actual assessment. The assessment was all done in quite big groups, and involved a mock product launch meeting and a task I remember doing at school, which involves convincing the room to take items from a list after you've been 'stranded'.
There was also a 'group interview', which was just sitting with 4 candidates and 1 interviewer for an hour, listening to the others get interviewed for a total of 15 minutes and then answering questions yourself while 3 others watch. It was very strange and I got the impression it was a cost-saving exercise rather than its own form of assessment.
They also didn't pay travel expenses for the first assessment day, which I've never heard of from any other company. Compared to other PR assessment days I took part in it was the longest, the worst organised and the tasks were the least relevant to actual PR work.