Signalling the new approach, Kerry McCarthy, the shadow Environment Secretary, said pollution levels were "critical" to any decision about airport expansion.
The Delhi-based independent environmental watchdog, the Centre for Science and Environment (CSE), said pollution levels in the city had "gone up manifold".
Sunil Dahiya, a campaigner from Greenpeace India, said air pollution levels had spiked in recent years.
The WHO says daily pollution levels should not exceed an average of 25 micrograms per cubic metre of fine particulate matter.
In recent days, one reporter at the news conference remarked, the hazy air has seemed polluted, though the environmental agency's daily figures say the pollution level has been low.
"The government's new plan says pollution will not fall to legal levels till 2025.
Government says pollution has degraded China's environment to a critical level, threatening health and social stability.
Defra said air-pollution levels on Wednesday were expected to reach eight or nine on a 10-point scale in much of southern England, the Midlands and southern Wales.
The group said that high pollution levels caused exposure to microscopic dust that embedded itself in the lungs, leading to increased hospitalization for asthma, lung disease, chronic bronchitis and heart damage, and that they could cause lung cancer.
Doing so, the group said, will not cut pollution levels around the highest-polluting power generators, where poor air quality has been linked by some studies to increased levels of asthma and other illnesses.
