Gordon Brown's recent pledge to invest £1bn in making thousands of homes more energy efficient provided some relief for householders struggling with soaring gas and electricity bills. But they are not the only ones who could benefit from this initiative. Investors are also being encouraged to plug into the potential of the energy efficiency sector.

Energy efficiency companies include those making "greener" lightbulbs, batteries, fans and lightweight motors. So, measured as a sector, the biggest companies have a combined market capitalisation that is estimated at $390bn (£218bn) and include companies such as Siemens and Philips.