I only recently purchased my first home so this deal has only just been made aware to me. We're with Npower so for the sake of argument, I've posted this deal for Npower but check with your current supplier as it seems most energy suppliers offer the same deal available till the end of November/December this year.
Essentially you get free loft and cavity wall insulation for your home. Offer open to vast majority of households so it's worth looking into and applying if you haven't already. You can save up to £175 for loft and £135 for wall insulation per year for free. You really can't go wrong!