Hi Alfi,
I would say the local fire officer (if appointed under Article 27) speaks on behalf of the enforcing authority even if he is talking total cobblers (I do accept there are some that do talk total cobblers) and therefore his written words would go a long way to provide a possible "defence" for the RP (Article 33) in the event of an "offence" (Article 32) being committed by him in relation to this matter.
In this particular case it appears that the fire officer is talking about a specific breach as he refers to it in a singular tense (i.e. "this gap" and "the gap") and this suggests to me that he has been given more information than we have been given in this post.
From the information I have seen in this post I would say that the fire inspector has made it quite clear that he is of the opinion that in this specific case, with regards to this specific gap, the fire authority does not believe the risk posed by the gap is sufficiently significant in terms of life risk to warrant them taking enforcement action under the RR(FS)O2005.
The fire officer is most certainly not saying that there isn't a gap, that this gap isn't a breach in FR construction that was required by the Approved Document B/Building Regulations 2010 (for which the fire authority is not the enforcing authority) nor that there would be no benefits in making good this breach (he even gives examples benefits, some of which are outside the scope of fire safety).
The RR(FS)O2005 is risk based and not prescriptive legislation and I personally see no mixed message(s) on the part of the fire officer or the fire authority with respect to this matter.
Furthermore, I eel the need to clarify a point someone else made on this thread, in that not all plantrooms are
required to be enclosed by FR construction as not all plantrooms are "areas of special fire hazard" (as defined by the Approved Document B).
Notwithstanding the above, please remember that other opinions are available.