My own experience was negative, but I have described my experience as neural. This is because I felt the interview process was quite fair in general, and the assessors were fairly welcoming.
After having my application accepted and passing various online psychometric tests, I was invited to an assessment day in Spring 2016. The day consisted of the following:
Re-sitting the numerical aptitude test.
A 10 minute presentation about yourself, your qualities and what you can bring to RR.
A team exercise - building a bridge and attempted to get a ping-pong ball and marble to the other side. The task lasts about 45 minutes.
A competency based interview (this followed my presentation).
The technical interview, which lasts about 45 minutes.
I felt I was having a good day until the technical interview. As a chemistry graduate I was eligible for this scheme, but my advice would be to not apply for this scheme unless you have an engineering degree or know a lot of about jet engines etc through your own interest. These were the types of questions they were asking me i.e general engineering questions. Nothing on Nuclear Engineering itself, which is what I spent much of my preparation time revising.
A final tip - have questions prepared to ask the interview about Rolls-Royce and their experiences with the company. I had done so and I believe they expect this as part of the interview. Even if they don't, it doesn't hurt to show further interest in what the company is like.
Hopefully you can do better than I did. The HR department give everyone feedback on their performance. Mine was described as 'not a bad day, more of an average day where you didn't stand out enough'. Probably a fair summary in hindsight. Good luck.