First, there was a 45-minute video call interview. After passing that, I was invited to an in-person written assessment at their office in Piccadilly. The assessment tested: how quickly I could understand software I hadn't used or seen before; if I could catch discrepancies in data; my Excel skills; Python skills; arithmetic skills; and mathematical proofs. I believe it could be tailored to the skills you (say that you) possess. After that, they told me they'd be in touch.