People who suffer from lung and heart conditions are being warned as pollution reaches very high levels in the UK.
The elderly and people with health problems have been warned to avoid strenuous activity because of harmful levels of air pollution expected to blanket parts of the UK.
The warning comes as forecasters say Britain could enjoy the hottest day of the year so far, with parts of eastern England predicted to reach highs of 22C (71.6F).
Eastern, central and southern England are forecast to be affected by “high” pollution today.
Parts of East Sussex and west Kent are expected to reach “very high” levels, according to the Government’s UK-Air monitoring service.
The high levels are due to domestic soot particulates, combined with dirty air from the Continent and some Saharan dust.
With the fine, settled weather conditions the pollution will be trapped over the UK for several hours.
Dr Sotiris Vardoulakis, head of the air pollution group at Public Health England, said: “While most people will not be affected by short term peaks of air pollution, some individuals, particularly those with existing heart or lung conditions, may experience increased symptoms.”
Dr Vadoulakis said in areas with very high pollution levels people should reduce physical exertion if they develop a cough or sore throat.
He added: “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.”
Winds are expected to pick up in the early hours of Saturday morning, bringing fresher air to all parts of the country.