The process was very straightforward. I applied with a CV and cover letter, then I received an invitation to an interview. The interview itself was split into two parts. The first was a written process, where I was given a problem and relevant questions, in order to be submersed into the role of a scientific advisory and test how I would approach the job. This exercise was also used as a way of ensuring I coherently wrote down my thought process, which was required for the second stage of the interview. Here, I talked them through the ideas and conclusions I had made in the first part, answered relevant questions, and also underwent a traditional interview.
I was living abroad at the time and had travelled to London especially for the interview, and despite everything, I never received any follow-up communication from Which? regarding the interview. I even emailed and wrote to them asking for some information. Having received follow-up communications from companies much larger that Which?, there is no excuse for showing such disrespect to applicants. Sadly my opinion of Which? has now decreased dramatically, as I believe them to be extremely hypocritical for reviewing and judging other companies and institutions while they themselves fail to maintain these standards.