The British Gas Home insulation scheme offers:
*Until 30th November 2012, British Gas is offering free loft and cavity wall insulation to anyone, even if you're not a British Gas customer.*
Subsidised cost of cavity wall insulation £249, loft insulation £225.
For British Gas customers receiving income or disability-related benefits - or aged 70 or over, the above is free.
As for CERT (see above)
0845 9717731 quoting ‘GID’ British Gas in partnership with Rockwool.