Oil importing countries should implement emergency oil saving policies if supplies fall by as little as one to two million barrels a day (b/d), the International Energy Agency (IEA) will warn next month.

The figure is much lower than the official trigger of 7 per cent of global oil supply - equivalent to six million b/d - agreed in the treaty that founded the energy watchdog for industrialised countries after the oil crisis of the 1970s.

A fall in supply of just one to two million b/d would be equivalent to the disruptions during the 2003 Iraq war or the 2002 oil industry strike in Venezuela.

A warning to set up "demand restraint policies" in the transport sector, such as driving bans or shorter working weeks, is contained in a study to be published next month during the annual IEA meeting of energy ministers.

It comes as oil is trading at more than $55 a barrel, and highlights the agency's concern about the possibility of a supply shock, the economic impact of high oil prices, and the need to focus on conserving energy rather than simply encouraging higher production.

The report marks a departure in IEA policy, as it says demand restraint measures, until now confined to times of crisis, "may be attractive during extended periods of high oil prices to relieve demand pressure".

In a draft of the report circulated to governments, it suggests dramatic measures, such as reducing motorway speed limits by 25 per cent, shortening the working week, imposing driving bans on certain days, providing free public transport and promoting car pooling schemes.

Investment in such schemes will be needed before any crisis occurs, the IEA says.

"A reduction in IEA transport fuel demand of even a few per cent could have a substantial damping effect on surging world oil prices," says the report, entitled Saving Oil in a Hurry.