In July 2004 I installed Extapol polystyrene blocks under the floor. It's not a nice job under the house. I'd rather never have to do that again.
Next I installed "Sissilation" (aluminium reflective and moisture barrier) below the polystyrene blocks. According to the man from Negawatt I talked to it probably doesn't make much difference whether the sissilation is above or below the polystyrene.
The overlap sealed between the sheets of foil was sealed with with alumunium tape. As per the recommendations form the Negawatt guy - I covered up all the ventilation holes in the sissilation so that it creates a moisture barrier.
Note: Negawatt use a product that looks like heavy duty bubble wrap with foil on both sides. It is stapled under the joists and seams sealed with aluminium tape - this creats a moisture barrier and also means there is a pocket of air between it and the underside of the floor (the width of the joists).
Most of our house has carpet which is not frigid on winter mornings. The bathroom floor is wood - so that's a bit cooler - but still fine most of the year.
Black polythene moisture barrier on the ground to fully block moisture rising into the house. This may be an overkill, given that I already have sissilation (aluminium foil) stapled to the bottom of the joists. However the ground is moist all year round so I would like to completely eliminate ground moisture as a factor.