New car models will have to pass real world driving emissions tests before being allowed on UK roads from Friday.
The tougher rules are being brought in across the European Union as concern over the harmful effects of nitrogen oxide has grown since the Volkswagen diesel scandal.
Vehicles have previously only been tested in a laboratory on a rolling road, but will now also face a 90-minute test involving a combination of urban, rural and motorway driving while equipment is attached to exhaust pipes.
The new test is designed to stop manufacturers cheating emissions tests.
Volkswagen Group fitted software to diesel models which manipulated examinations by detecting when the vehicles were on a rolling road.
The manufacturer said 11 million of its vehicles were affected worldwide – including almost 1.2 million in the UK.
A Government testing programme last year found that modern diesel cars emit six times more nitrogen oxide in the real world than in the lab.
Under the new rules, manufacturers will have to slash those emissions by two-thirds – but they will still be allowed at a higher level than acceptable laboratory limits.
A further reduction in emissions will be required from September 2020.
Air pollution causes an estimated 40,000 premature deaths a year in the UK and is linked to health problems from childhood illnesses to heart disease and even dementia.
Transport minister Paul Maynard said: “We are taking strong action to clean up our air and these tough new emissions standards will reduce dangerous pollutants.
“This Government has led the way in Europe pushing for on-road emissions tests, alongside a tough new laboratory test, to clean up air in our towns and cities.
“This will ensure all vehicles meet rigorous standards when driven on our roads and we are going even further, tightening requirements again in 2020.”
Last month, the Government announced that new diesel and petrol cars and vans will be banned from 2040 as part of efforts to tackle air pollution.
It also pledged to work with local authorities to developing targeted diesel scrappage schemes.
Environmental law firm ClientEarth, which took the Government to court to force the action on air quality, described the introduction of road-based emissions tests as a “vital step”.
But it claimed UK ministers “colluded in a deal at EU level” to allow the motor industry to emit double the existing laboratory legal nitrogen oxide limits “for years to come”.
Steve Gooding, director of motoring research charity the RAC Foundation, said the new test “can’t come soon enough” for car buyers who doubt what the automotive industry tells them.
Jim Holder, editorial director of What Car? magazine, said the Volkswagen scandal highlighted how previous legislation for vehicle testing was “woefully inadequate” and believes the new regime will “go some way to reassuring motorists”.
But he claimed the Government has “muddled its policy” over diesel cars by using “rhetoric to damn its environmental credentials” while reducing grants for hybrid and electric vehicles.[“Source-timesandstar”]