Road hauliers are unhappy with the scheme, saying compliance will be expensive, but transport officials say improving the air quality will help millions of Londoners, especially those suffering from asthma and other respiratory problems.

Low emission zones are already planned or in operation in 70 towns and cities in eight European countries including Norway, the Netherlands and Germany.

"This will be the first in Britain and the largest in the world by a significant margin," said a spokeswoman from Transport for London, which will run the scheme.

"London's air quality is the worst in Britain and among the worst in Europe. Levels of particulate matter in many parts of London are way over EU standards," the TfL spokeswoman said.

"It will help improve the quality of life for people suffering from asthma, cardio-vascular conditions and all the conditions that particulate matter exacerbates," she said.

The capital already has a congestion pricing scheme, a charge on vehicles entering the city centre, but that was aimed at reducing congestion rather than cleaning the air.

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 square kms (610 sq miles), far bigger than Hong Kong.

PHOTOGRAPHS AND FINES

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 2008 and to larger vans and minibuses in October 2010.

Road hauliers are not happy.

"We realise that the mayor has a statutory duty to improve the air quality of London but we don't think the scheme as proposed will be effective in achieving that," a spokeswoman 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," she said, noting that exhaust scrubbers cost up to 5,000 pounds.

All lorries made after October 2001 automatically comply with the Euro 3 standards of particulate emissions of 0.05 grammes per kilometre, the level adopted by the scheme. TfL said it identified 120,000 lorries of over 12 tonnes inside the zone during six months of monitoring last year, and estimates 10 percent do not meet EU standards. Lorries that do not comply and have not been retro-fitted with exhaust scrubbers to bring them up to standard will be charged 200 pounds a day to be in the zone, with a penalty of 1,000 pounds if they fail to pay.

The scheme cost 49 million pounds to set up but is only expected to raise 2 to 3 million pounds a year in daily charges and a further 1 million pounds in penalty fees.