Hi rossko,
Thanks for the reply. Regarding the power, I was going to use a siemes cable in the case of a coax cable or else passing power through the UTP cable as you said.
As for the waterproff cable, cable tied to the conduit; my wiring is internal. I have maybe 6m running on the outside than the remaining 25m running inside my apartment (my apartment is a bit elongated). Also the roof conduits were passed on the floor of the apartment on top of mine so they are not accessible.
Using shielded UTP could be an option too (I assume the shield would be connected to PE to shield noise originating from the mains cable). Only concern would be flexibility of the cable to pass 2 of them through a single 20mm conduit (although the same thing could be said about an RG59 seimes cable). An advantage of using UTP / shielded UTP would be of having extra conductors also for a pick up or to use the entire cable if the cameras are changed for IP version.
One other option that came to my mind was that of passing the cable in the corner between the roof and the side wall and maybe (some day....) hide them with coving (could also use this option with the UTP cable_.
As you can see I'm quite confused, with a lot of options but few knowledge about the outcome in order to make a decision. Most probably, the best option would be a UTP cable passed in the corner behind coving, but was hoping to not have to make coving just to hide the cables.