Hi, I don't know how well it acutally works as I am not a home-owner and have not looked into it in that respect. My uncle told me that he noticed much more of a difference having Loft insulation installed than when he had Cavity Wall insulation installed later on.
The reason I'm replying, is that I work for a company who install cavity wall insulation and loft insulation. The company I work for can get grants from various utility companies (on behalf of a government energy efficiency scheme), so if you can tell me a bit of information about yourself and your house I can give you idea if your quote is reasonable (i'm not a salesman, but i can tell you if you have been quoted over the odds)
First off, we have some contracts where its free to people who are on certain governement benefits, so do you recieve any benefits?
Detached or Semi or Mid-terrace?
House or Bungalow or Flat?
How many bedrooms does it have?
How old is your house?
What is your utility company for electric/gas?
Finally: I can work out what we would charge a customer, with a standard house, with that info. But if your house is bigger than the norm (for its type) then there would be additional charges, so is your house particularly large?