Originally Posted by neddyuk
...With the mornings getting colder it seems to take a while for the heater matrix to warm up...
Exactly! It's all relative. The colder it is outside the more the outside air has to be warmed, but your engine will only heat up at whatever rate it will heat up at, depending on how it's driven. And as DXB says, it's down to the engine coolant to provide that heat source.
Pop your air recirc on so that you are constantly warming the air in the cabin, not the colder air outside - that will help. But beware that this could make your windows steam over though...