Parts of the country could reach the highest level of air pollution today (Friday), prompting health warnings.
High levels of pollution across the UK, as still, warm conditions create a build-up of local pollutants from sources such as traffic fumes, combined with pollution from the continent and Saharan dust from the south.
The warning comes as forecasters say today could be the hottest day of the year so far, with temperatures reaching 20C.
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 from the early hours of Saturday morning, bringing fresher air to the country.