How cold is cold? If the air is just "medium-warm" as opposed to "not heating up at all", the engine might not be loaded heavily enough to generate enough heat through your entire journey.
My mk3 jazz (non hybrid, of course) never really blows hot at this time of year if it's working at light load. The engine just isn't generating enough heat and the cooling system will sacrifice interior temperature to keep the engine warm.
So that's conditions like driving around town or keeping a steadyish 40mph on a flat country road (not much load, lots of cold outside air passing through the engine bay).
If you're confident that you're not losing coolant, I'd suggest bringing it up to 70mph on a motorway, or finding a hill to drive up. That'll make the engine work a little bit harder, and if the air starts blowing properly hot, there's probably not too much to worry about,
