It is a qualification, gained after a course of online study. You have to answer 30 multiple choice questions. It is slightly tougher than the exam you took to get your flyer and operator id but, if you have taken a course and practiced the mock exams the real examination holds no surprises and is easy to pass.
There is a bfo thread about it here
You could also investigate Article 16 Authorisation, available through membership of an organisation such as FPVUK or BMFA