ON more than 20 different occasions in the past five years, Glasgow has experienced high-level pollution alerts.

Critics say few people were notified of the dangers of toxic smog clouds as Defra, the ministry responsible for alerting the public, relied on tweets and advice on its website to tell people. The website only receives a few thousand hits per month.

Even when the pollution, mainly caused by diesel fumes, hit level 10, the highest category, it issued no extra warnings to the media or public to avoid exercise or going outside.

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Britain was hit by a level 10 pollution cloud recently but the new figures, collected by Defra but never previously published, reveal a number of areas across the country, including London, Manchester and Swansea, were affected many times before by similar levels. Data shows there were 94 days between April 2009 and April 2014 when smog reached high levels of seven to nine, when people with asthma, heart and lung problems are advised not to exercise and avoid travel.

Scientists, including Defra's own advisers, ­criticised the department for failing to issue adequate warnings when Britain was hit by smog.

Professor Frank Kelly, chairman of the committee on the medical effects of air pollutants, accused ­ministers of "political ­indifference" in relation to the 29,000 premature deaths the committee estimates are caused each year by air pollution.

"The costs to society from poor air quality are on a par with those from smoking and obesity," he said.