With temperatures set to hit the 25C-30C in the coming days, a toxic smog from the continent could come with it, with the south of England worse affected. According to the Met Office, temperatures are likely to peak on Tuesday, 16 August.

The UK government's air pollution forecast indicated moderate levels of pollution in parts of England and Wales. However, it did not appear to be as widespread as was previously forecast in May this year.

The Department for Environment, Food and Rural Affairs (Defra) air pollution forecast said on Saturday, 13 August: "Air pollution levels will be predominantly Low at first, but areas of moderate air pollution are expected to develop across parts of southwest England, Wales, and Northern Ireland during Tuesday and Wednesday as a continental airflow develops."

Summer smog – or photochemical smog – is caused when nitrogen oxides, usually present due to car exhaust or industrial emissions, react with hydrocarbons in sunlight to form airborne particles and ozone. As such, it is most likely to impact on major cities or industrial areas, such as London which has seen episodes in recent years.

Although smog was common in London prior to the Clean Air Act of 1956, the great smog of 1952 is the most famous, after it killed thousands in just one day. Although such incidents have become a thing of the past, a study conducted last year by Kings College London's Environmental Research Group on behalf of Transport for London, suggested that pollution in London could claim up to 9,500 lives a year. London has the world's highest measured levels of nitrogen dioxide – the gas that causes smog – and has breached EU safety limits every year for the last five.

Nitrogen dioxide can have detrimental health impacts, according to Defra, particularly on those with heart and lung conditions. It said that those in a good state of health were unlikely to experience short-term impacts, though periods of elevated pollution levels could cause respiratory problems as well as heart disease and cancer.