High levels of nitrogen dioxide - which brings on respiratory disease, and is one of the main factors in the asthma epidemic - settled over four of the country's biggest cities for many hours on 23 December and Christmas Eve.
The Department of Health is being pressed from within Whitehall to set up an inquiry into how many people died or became ill because of the smog - the worst since a similar episode in London three years ago, which was subsequently found to have killed 160 people.
The black Christmas will strengthen the resolve of ministers who are putting the finishing touches to far-reaching measures that will enable local councils to restrict or ban traffic from areas of towns and cities in order to combat air pollution. The measures, aimed at attacking the new smogs in the same way as the Clean Air Acts gradually eliminated the pea-soupers of the 1950s, will be announced this month.
The holiday smog, which follows the most polluted summer this decade, reached dangerous levels when nitrogen dioxide emitted by a rush of cars on last-minute Christmas errands failed to disperse because of a temperature "inversion", when cold air near ground level is trapped by warmer air higher up.
The gas reached 198ppb (parts per billion) in east Birmingham on 23 December, nearly treble the previous record for the year, and 257ppb in Walsall, about two and a half times as bad as previously.
High levels were also recorded in Leeds and Manchester. London suffered worst, with two days of pollution twice as bad as anything that had been encountered all year. Over 23 December and Christmas Eve there were 27 hours of serious nitrogen dioxide pollution over much of the centre of the city. The highest level of all, 288 ppb, was recorded near Victoria.
The crisis passed on Christmas Day as the traffic died down and winds dispersed the pollution.
At no time during the crisis did the Government issue health warnings to advise people with respiratory trouble to stay indoors or ask drivers not to take out their cars - even though it had issued them during the polluted summer.
The Department of the Environment said yesterday that it had not warned the public because it thought that the weather was going to change earlier than it did.
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