London air pollution
London is to be hit by a continental dust cloud as the city heads to the polls to vote for the next MayorDan Kitwood/Getty Images

The British government has issued a warning over air pollution as a dust cloud from the Continent is expected to hit London on 5 May, the same day that Londoners head to the polls to vote for the next mayor of London.

The Department for Environment, Food & Rural Affairs (DEFRA) has issued a warning for moderate air pollution for most of England and Wales as south-easterly winds from the Continent dominate throughout the day. The dirty air is expected to remain in the UK's atmosphere for three days, with the possibility of the air pollution alert rising to "high" at times, particularly over the weekend.

The government health advice for moderate air pollution warns that adults and children with lung and heart problems should consider reducing vigorous physical activity in outdoor environments. Those who are particularly sensitive could also experience health effects during low air pollution days.

In the case of air pollution levels rising to high, government health advice states: "Adults and children with lung problems and adults with heart problems, should reduce strenuous physical exertion, particularly outdoors, and particularly if they experience symptoms. People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion."

The warning also notes that those who experience discomfort, such as sore eyes, coughs or sore throats should reduce their outdoor activity. The worst of the Continental dust will be seen on 8 May across a majority of the UK, particularly in coastal regions in Wales and much of the Midlands.

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The air pollution warning came as mayoral candidates Zac Goldsmith and Sadiq Khan were urged to tackle air pollution in their policies. Research conducted by ClientEarth in March showed that three in four Londoners believed the Mayor has a "moral responsibility" to clean London's air.

James Thornton, Chief Executive of ClientEarth, said: "The Mayoral candidates must listen to Londoners and come up with proper plans that will reduce air pollution as soon as possible, so we are not choking on illegal levels of pollution until 2025. The time for excuses is over."