These are estimates based on insulating a gas-heated home with either a totally uninsulated loft, or topping up existing insulation from 100mm to 270mm. (The recommended depth for mineral wool insulation is 270mm but other materials need different depths). *Average unsubsidised professional installation costs, although these will vary.
If your loft is already insulated, it's worth checking that you've got enough insulation to get the maximum saving. If everyone in the UK installed 270mm loft insulation, we could save nearly £210 million – and almost 1 million tonnes of carbon dioxide every year, the equivalent of taking nearly 364,000 cars off the road.