It sounds like cold calling to me, fran. Unless you have applied for a grant for insulation, how would they know that you might be interested?
They are a nationwide company with a website
http://www.nesuk.com/ - but personally, if I were going to have this work done, I wouldn't offer the work to someone who just rang up. Many companies can access these grants and if might be advisable to seek alternative quotations from local companies or who have done this for your neighbours. You might like to read this first, about grants and if you might be eligible
http://www.energysavi...-for-all-householders
If it were me I would worry that if I'm not eligible, they'd try to sell it to me anyway.
I may be sceptical but I don't ever take offers from people who cold call me.