The morning after Deepavali, the Hindu festival of lights, residents of New Delhi woke up under a blanket of toxic smog and breathed in the most dangerously polluted air of the year so far, after revellers, as usual, defied a fireworks ban.

New Delhi has the worst air quality of all world capitals, but even by its sorry standards, today's reading was extra bad, as people paid the price for celebrating India's biggest festival in the noisiest and most smoky way...