Saharan dust is contributing to unusually high levels of air pollution, threatening the health of elderly and vulnerable people in the UK.

Parts of eastern England, the Midlands and Wales during last week experienced the highest levels of air pollution on the government’s official scale, and those with heart and lung problems have been warned by environmental experts to avoid "strenuous activity".

The Department for Environment, Food and Rural Affairs (Defra) said certain areas would reach 10 out of 10 - or “very high” - on its air cleanliness chart and visually, the skies looked yellow/brown and overcast.

When levels reach 7 to 9 on Defra's chart, adults and children with lung problems and adults with heart problems are advised to reduce exertion.