The answer in short is no. You are not the "responsible person" see below extract from the Regulatory Reform (Fire Safety) Order 2005:

Meaning of “responsible person”

(a)in relation to a workplace, the employer, if the workplace is to any extent under his control;

(b)in relation to any premises not falling within paragraph (a)—

(i)the person who has control of the premises (as occupier or otherwise) in connection with the carrying on by him of a trade, business or other undertaking (for profit or not); or

(ii)the owner, where the person in control of the premises does not have control in connection with the carrying on by that person of a trade, business or other undertaking.

You are under the regulations:

Safety assistance

Originally Posted by: Hsquared14

Bearing in mind Woolf's definition I would say no because you are only there on a temporary basis, esssentially you are "helping out" whoever is the responsible person for the site.  The responsible person is basically the most senior person on site who delegates certain duties to other people. That is the position you are in.

I 100% with the above I'm a member of the IFSM its the top dog on the site show him this I'll happily put him / her right

Its relatively straightforward in most premises as there is a heirachy 

1) If there is an employer, then he is the Responsible Person. This does not need to be a named person, but a corporation susvch as Ocado PLC

2) Where there is no employer - say a block of flats - it is the person with control of those premises. This could be a local authority, a landlord or managing agent 

3) If there is no person in control, its the owner of the premises

Beware of Article 5(4) which allows anyone with a responsibility for maintenance or safety to be treated as a Responsible Person insofar as their duties apply

So a Safety Officer or Fire Alarm Engineer could be prosecuted under 5(4) as the RP in some circumstances. At least one Fire Alarm Engineer & Fire Risk Assessor have been prosecuted nuder this Article.

Its worth noting that The London Fire Brigade considered prosecuting the  Branch Manager of the infamous New Look store in Oxford Street under Article 5(4), but the legal people said they had enough to prosecute so dropped that angle

Be very careful

So in answer to the OP, he could be considered as a Responsible Person under 5(4) but is not THE Responsible Person  which is the employer

Originally Posted by: David Thomas

How many safety managers are even competent to assist in fire safety matters..?

Define what competence would be required to assist in fire safety matters..