You no longer need to hold the ROCC to be an AFISO, just have passed the exam and practical. I think the change was introduced a few years back after the CAA reviewed CAP 1032 and meant that the AFISO didn't need to have the extra expense of obtaining the ROCC itself.
Bear in mind that the 2 UK colleges provide training in ATS and ATM with FIS and ATC Service being part of ATS. No UK college provides a CAA approved FISO course but I'm intrigued to find out what this organisation is providing.