Hi LSB,
I'd second what PeterW says about the superfoil in floors! Yep the manufacturer will tell you it can be done and granted it'll give you a bit of insulation but it won't be effective.
Back to your original question(s)...
Presumably you don't have an insulated cavity wall if you are considering IWI (internal Wall Insulation)?
You can attach plasterboard to your block wall in various different ways. The two most common are:
"Dot and Dab": This is where you use adhesive and put a number of lumps on the back of the board and then stick it to the wall.
Battens: Screw battens to the block work and then screw the plasterboard to the battens. Using this method you can more easily insulate between the battens and then also attach a layer over the top. Either as an individual layer or using insulated plasterboard. You do also need to incorporate a vapour barrier.
Alternatively, you can plaster the block work. Firstly with something like Thistle Hardwall or Thistle Bonding (depending on what the blocks are) as an undercoat and then a second (finish) coat is applied such as Thistle MultiFinish.
If you use the plasterboard method, you can tape the joints on the plasterboard (tapered edge board not square edge) you then use a jointing compound and sand it down to get it smooth. See here. Or, you can apply a skim coat of plaster. The skim coat will give you a much better finish but does cost more.
