The biggest beneficiaries of Gordon Brown’s energy measures look set to be loft laggers, double-glazing installers and other home-insulation specialists. The package offers the prospect of windfalls for the tradesmen and companies that make a living in this growing sector.

But it is a godsend, too, for the poorest households who will have the work done free. The better-off, who may have to contribute, will benefit from lower heating bills.

Loft insulation is a good starting point. It prevents 15 per cent of heat loss through the roof, by trapping heat inside the house. A 270mm layer of insulation costs £500 to install but average savings are £155 a year. DIY insulation costs about £250, with payback after two years.

Insulating cavity walls can save one third of heat loss from a home and reduce bills by 15 per cent or £120 a year. Only homes built after about 1920, however, were constructed with two layers and a cavity. Installation costs are about £500 and payback takes about four years. Older houses can be fitted with solid insulation: either a weatherproof extra external wall or an extra layer of plasterboard inside. External work is expensive. The average cost for insulating a three-bedroomed semi is £4,500. Annual savings will be about £380, so it takes 12 years before payback. Internal insulation works out at about £42 a metre, saving £360 a year.

Double glazing is not to everyone’s taste but can cut heat loss from a room by 50 per cent. Costs vary from £300 to £1,000 a window depending on size. Experts advise starting with windows in rooms that are most expensive to heat. Savings are about £110 a year.

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