Kurnal, i agee totally, the 'relevant person' concept has become a bit of a red herring. and more importantly, i think it has clouded the Fire Authorities view of what they can/should be doing.
I also agree that they are in a stronger position than they think they are, or maybe choose to be (I think that may have something to do with the near obsession some FRA's have about not being perceived to be prescriptive).
But remember, the fire authority are only consulted. our opinions can be disregarded by the BCO or AI. so the FRAs course of action from this point is to either take the view of 'well we told you our position, if you choose to ignore us then you have taken ownership of the risk'. which is a bit of a cop out if you ask me. or, Invoke the BRegs and FS procedural Guidance and make it clear to the client that they will enforce retrospectively. this should be done used much more than it is, and is what i think you mean by 'they have the tools'. Unfortunately for what ever reason its not.
to be a little controversial. some FRA's tell their Inspectors to just comment and send it back without any follow up, whilst enforcing the philosophy that 'because we are only consulted we have no powers so the process is merely lip service. But don't worry we'll get them under the RRO'. Some IO's i've met have never even heard of the BRegs and FS procedural Guidance.
Come to think of it i've met a number of AI's that haven't as well.