The Department for Food, Agriculture and Rural Affairs has warned there are high levels of pollution in the south east, London, Yorkshire and Humberside, and East Anglia:
Defra ranks air pollution from one (the green areas) to 10 (marked in purple), with one being the lowest and 10 the highest.
Norwich was among the cities covered in smog this morning as health experts warn those with heart and lung conditions, including asthma, to avoid strenuous activity outdoors.
People suffering symptoms of pollution - including sore eyes, coughs and sore throats - should also cut down the amount they do outside, experts said.
Record levels of air pollution will continue to parts of the UK, with pollution levels already reaching level nine - high - this morning in the south east, Greater London and eastern England.
Defra ranks air pollution from one to 10, with one being the lowest and 10 the highest.
"Very high" levels of pollution are also forecast later today for the East Midlands.
The Environment Agency has issued a flood alert in the Anglian region as heavy rain is forecast across Britain.
A flood alert warns people in the area that flooding is possible and they should be prepared.