"Office ICT used around 988 GWh or 11 percent of all commercial electricity use. Together, this represents 3 percent of the total electricity demand in 2010."

Testing a number of computers by Australia's Department of Climate Change and Energy Efficiency has uncovered wide variances between best and worst performers in power consumption, the report says. The best small desktop had a consumption of 17.6 watts and the worst 99 watts - more than five-and-a-half times as much. The best of the largest class of desktops consumed 67.9 watts and the worst 162.8 - a multiplier of 2.4.

The worst of the powerful notebooks consumed 37.4 watts and the best 9.8, so there is considerable room for improvement, EECA argues. One significant factor is the presence or absence of an automatic power-management tool in the computer which would switch off components when not in use.

Under a do-nothing option, manufacturers would overall still reduce consumption owing to improved technology, but the saving would still be "lower than is readily and cost effectively achievable".

A voluntary scheme, with labelling to assist the buyer in making a decision, would fail, EECA suggests. "The tendency under a voluntary scheme would be for only the better-performing products to be labelled, meaning that there would be no basis for consumers to compare between poor and average performance."