Article 5 of the RRO states,
(3) Any duty imposed by articles 8 to 22 or by regulations made under article 24 on the
responsible person in respect of premises shall also be imposed on every person, other than the
responsible person referred to in paragraphs (1) and (2), who has, to any extent, control of those
premises so far as the requirements relate to matters within his control.
(4) Where a person has, by virtue of any contract or tenancy, an obligation of any extent in
relation to—
(a) the maintenance or repair of any premises, including anything in or on premises; or
(b) the safety of any premises,
that person is to be treated, for the purposes of paragraph (3), as being a person who has control
of the premises to the extent that his obligation so extends.
I understand this to mean that fire safety consultants will have a degree of legal liability, subject to the ususal burnden of proof, if they give manifestly poor advice.
It definitely covers those such as fire alarm engineers who have a contract to maintain and can be shown not to have diligently done so.
This doesn't mean that the employer/owner etc has no responsibility though they would be on strong 'due dilligence' ground if they contracted a recognised expert firm.