loose fill insulatiion

[dada]

i currently have a conservatory that has 8 bricks above dpc. 2in cavity. the conservatory bit is coming down and we're building on top of it.
the bldg regs chap has said we need to full fill the cavity then use insulated plasterboard.
trouble is, when we take the conservatory down i suspect there may be a fair amount of mortar in the cavity that could make it difficult to push in isolwool sheets.
so, i was sondering if there was anything you can buy (like polystyrene beads) that i could just poor in to fill it insterad (a bit like cavity wall insulation stuff, but in my case poored in not pumoed in ?)
thanks

 

[noseall]

if the cavity is as congested as you say, it may be prudent to remove the internal blockwork and start again.