Article 26(1) gives their fire authority the direction that they must enforce the legislation and that they may appoint inspectors (cant see how they could otherwise!).
if all persons attending are appointed IOs by their brigades. Then they all can exercise their own powers within Article 27.
But if you take along a trainee that does not have signed authority. you need the RPs permission for him to be there. And they can refuse. He has no powers of his own and his presence cannot be justified under article 27(1) as necessary for the purposes of carrying out this order.
If the person accompanying is an authority fire investigator. Then they could use their powers under the fire and rescue services act section 45 and 46
If the person accompanying the IO is from another agency ie. planning, licensing. more often than not, they will have their own powers of entry.
But. If the person accompanying does not have their own authority. For example. Scientific advisor or engineer. Then you, as an io, can cite article 27(1) 'an inspector may do anything necessary for the purposes of carrying out this order'.
For example 27(1)(f) refers to dismantling of articles within the premises. If you need an engineer for this. Then 'anything necessary' would reasonably include bringing a competent engineer to dismantle. 27(1)(e) could require a scientific advisor.
So. as long As the person accompanying is necessary to enable you to carry out your duties within the order then, under 27(1) they can be present to assist you.
The reverse of this is therefore quite clear. You can't just bring someone along 'for a jolly'
