My house was built in 2001 and has no cavity wall insulation, but the insulation listed on supporting paperwork was listed as "Thermal". The inner skin is thermal blockwork, but does it need full fill cavity wall insulation or are the thermal blocks sufficient to produce the required U value for modern housing? If not should I be able to approach the builder under NHBC to get a cavity fill?
Between now and 2016 the rules are changing, every year the insulation requirements become more demanding, moving towards the Passive House specification for new homes from 2016.
From 2016 houses will need to be almost air tight, a move to reduce the carbon footprint. Insulation and ventilation will need to improve. Merely adding blown cavity wall insulation will not get you to 2016 standard. Indeed, cavity wall insulation in most instances results in a colder home that will cost more to heat. The problem being that outer walls tend to leak water, the water makes the insulation wet, which in turn makes the inner wall wet and results in a heat bridge and increased heat loss.
Read up on Building regulations they are free on the net then decide what you would like to do.