The £49 million (S$136 million) scheme will use a network of cameras to monitor the emissions of large diesel lorries, later expanding coverage to smaller commercial vehicles, and impose heavy fines on those exceeding EU exhaust limits.

The new scheme will initially apply only to diesel lorries over 12 tonnes which have to comply with strict European Union limits on particulate or soot emissions from their exhausts.

The scheme will operate all day every day, and cover an area of 1,580 sq km, far bigger than Hong Kong.

Cameras at 75 sites in and around the zone will photograph vehicles' licence plates and heavy fines will be issued for non-compliance.

The scheme will be extended to lorries over 3.5 tonnes, coaches and buses in July this year and to larger vans and minibuses in October 2010.

Road hauliers are unhappy with the scheme, saying compliance will be expensive.

A spokesman for the Freight Transport Association said: 'It is costing the industry a huge amount of money to comply and some of the smaller operators will struggle.'

But transport officials say improving the air quality will help millions of Londoners, especially those suffering from asthma and other respiratory problems.

London already has a congestion pricing scheme, a charge on vehicles entering the city centre, but that is aimed at reducing congestion rather than tackling pollution.

REUTERS