Kiwi,
As far as I'm aware, the red-sheathed 2-Core TPS cable has the same properties as it's white-sheathed brother, ie: has a 600V/1kV rating, the only difference being that it has a Red outer sheath to denote the system as a Fire Alarm system.
Even so, it has a conductor size of either 1.0mm2 solid or 1.5mm2 stranded.
As Ray rightfully mentions, it is contrary to the Regulations to install a cable in Domestic Installations without an integral Earth conductor.
Having said that, I've worked in heaps of houses where the switch wire from the batten-holder to the light switch (in a 3-plated system) is only a 2-Core (Red/Black) cable.
Also depends on when the place was wired originally.
