People should be braced for "very high" levels of air pollution over the next few days, experts have warned.
The south-east will see high levels of pollution today, 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.
"The current elevated pollution levels over parts of the UK are caused by light winds allowing the build-up of pollution, plus dust from the Sahara contributing to pollution levels," according to the Defra forecast.
Experts are anticipating "high" or "very high" air pollution levels across much of England and Wales.
People suffering the effects of high levels of pollution - including sore eyes, coughs and sore throats - should cut down the amount of activity they take outside, experts have warned.
Asthmatics might need to use their blue reliever inhalers more often as they could be prone to attacks today and over the next few days. Other people with lung and heart problems, and those who are older, should also avoid strenuous exercise or activity.
The advice, from Public Health England (PHE), Asthma UK and the Department for Environment, Food and Rural Affairs (Defra), comes after a warning that people in parts of England should be braced for the highest level of air pollution recorded by Defra.
And the 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."