Cavity Wall Insulation Guarantee

Redlander

I had a survey for cavity wall insulation  in anticipation of getting a heat pump. Only the back wall of our 1960s terraced house has a cavity and the quote was based on 19.5 square metres with EPS bonded beads. There would normally be 25 year guarantee (costing £150) but there is a note stating "CIGA guarantee cannot be applied for as sufficient evidence was not collected during survey". I think this is because, when the next door house had their cavity walls done, no barrier was installed between the two houses and there is a possibiility that some of their insulation spilled across into our wall.

I am wondering what is the risk in going ahead without the guarantee. What sort of occurrence is being insured against and what is the worst-case consequence that I might find myself paying for?