Insulating an extension

[Rastanking]

Hi everyone,

I wonder if anyone has got any advice for me regarding insulating an existing extension, a kitchen with the bathroom above.

I have contacted a couple of companies that can offer free insulation, however when they have bored a small hole in the cavity wall and looked in with their boroscope there is some insulation in there already, it is the old style yellow material, I'm presuming that this is fibreglass, however it is very thin probably about 3mm max. Both companies say that because there is insulation in there they cannot add any more.

My question is why can't a company add new insulation to the existing, is there some form of legal legislation here or is it just the companies policy? If it is possible to add new insulation could anyone recommend a company within the Manchester/North West area.

Thanks in advance