My interview consisted of two stages.
Stage 1:
I got sent two translated texts, one in English, one in German, which I had to correct. I sent the corrected version back to RWS and then got invited for an interview.
Stage 2:
I went in for my interview in their Gerrards Cross Branch. After a tour of the premises, I got asked to do another translation review, this one featured a scientific report. After completion of this, I had my interview with the personnel officer.