Health experts are warning that people should be braced for "very high" levels of air pollution over the next few days.
The East of England and Midlands are the worst-affected areas but large swathes of England and Wales will see high levels of pollution, the Department for Environment, Food and Rural Affairs (Defra) said.
The elevated pollution levels have been caused by a combination of light south-easterly winds, the continental air flow and dust which has blown up from the Sahara desert, a spokeswoman said.
Defra has a ten-point air pollution index with ten being the highest level. Large parts of the East of England and the East Midlands are forecast to hit a pollution index of ten on Wednesday. This is indicated by the purple area on the map (above).
- Adults and children with lung problems, adults with heart problems, and older people, should avoid strenuous physical activity.
- People with asthma may find they need to use their reliever inhaler more often.
- Reduce physical exertion, particularly outdoors, especially if you experience symptoms such as cough or sore throat.
High levels of pollution are expected to continue across East Anglia and the Midlands on Thursday. But the air pollution is expected to ebb away by Friday.
Last weekend, some people found their cars to be covered in a light coating of red dust. The Met Office said that a large amount of sand and dust was swept up by storm winds in the Sahara Desert.
Experts said that the airborne particles of dust were blown north to the UK where they combined with our warm air and were deposited during showers.
A Defra spokeswoman said: "The high level of air pollution this week is due to a combination of local emissions, light winds, pollution from the continent and dust blown over from the Sahara.
"We want to keep improving air quality and have introduced a new five-day forecast service in addition to investing heavily in local and transport initiatives to tackle this issue head-on."