3 planks of wood in loft

[John D v2.0]

Yes that beam in the floor is probably a binder to split the span of the ceiling joists in half and stop them sagging. In turn, the binder itself needs support to stop it sagging in the middle. The simplest thing is to hang it from the ridge, as you can see those planks are doing.
So yes it's probably a structural part of the roof, and probably not for decoration. Just make them a feature of your car track...

 

[Chud]

Free advice about things that i didn't ask about and no answer to the question i asked about.

So...Question:

My question is what are they for? And can i take them away and put something else in instead?

Answer:

They are Hangers usually supporting Binders. Binders that keep the joists in plane.

Why they've been dropped in such positions is impossible to know without exposing below the ply flooring to see what and how they are connected to?
Until you know more leave them alone as suggested above.

Plus, presumably out of concern Vinn has highlighted some potential issues - yes, the salts may be on the chimney from prior to your roof refit but the windows..?