I had heard of H&S awareness officers, indeed the HSE have a leaflet on their role. But recently had a visit from an RCO at a top tier COMAH site. The visit was not chargeable and I was wondering if this was because it was an RCO and not an inspector!

RCOs are effectively HSAOs under a different name and are not warranted Inspectors. They do, however, tend to have more of a focus on regulatory issues such as following up on compliance with Improvement Notices etc rather than a mainly advisory role.