Air pollution levels were sent soaring on the hottest July day on record, with government alerts issued in three regions.
Sunny weather and temperatures as high as 36.7C (98F) resulted in moderate pollution across much of England, with dangerously high levels measured in Eastern England, the East Midlands and the South East.
Pollution levels in the West Midlands are also currently considered “High”.
The Department for Environment, Food and Rural Affairs (Defra) warned those vulnerable to the effects of pollution to be cautious.
On its website, Defra said: “People with lung disease, children, the elderly and people who are active outdoors may be particularly sensitive to ozone and may begin to notice respiratory symptoms, such as coughing and throat irritation.
“People with asthma are not necessarily more sensitive but, if affected, can use their ‘reliever’ inhaler to alleviate symptoms.
“If affected, people are urged to take sensible precautions such as reducing strenuous exercise. Individual exposure to ozone can be reduced by avoiding exercising outdoors during the afternoon, because this is the time of day when ozone levels are at their highest.”
Moderate levels of pollution are expected to remain throughout Thursday and Friday, before subsiding over the weekend.