High levels of air pollution are continuing to affect parts of the UK on Thursday, according to experts.
Data from environment department Defra shows London has reached the maximum level 10 – meaning very high.
Levels in eastern England have reached nine – meaning high – with the South East and north-west England, the Midlands and north Wales also affected.
Health warnings have been issued for people with lung and heart conditions, as well as for those with asthma.
The prime minister admitted the atmosphere in the capital was “unpleasant”.
The smog-like conditions, which are expected to clear on Friday, are caused by a mixture of local and continental pollution, and dust from the Sahara.
‘Risk of attack’
Defra (the Department for Environment, Food & Rural Affairs) has a 10-point scale for measuring air quality – with level one implying a “low” risk of air pollution and 10 for “very high” levels.
Levels in eastern England had reached level nine – meaning high – by Thursday morning.
“Moderate” levels are expected in parts of Northern Ireland and “many other parts of England and Wales” on Thursday, Defra added.
On Wednesday, levels were recorded at eight in parts of south-east England and East Anglia, with level seven in Greater London.
Levels are determined by the concentration of five pollutants in the air – ozone, sulphur dioxide (SO2), nitrogen dioxide (NO2) and two types of particulate matter.
High levels of air pollution are usually reached about five times a year.
BBC weather presenter Tomasz Schafernaker said: “We have to wait until the end of week before we see Atlantic winds coming in which will help to improve the quality of the air across the UK.”
David Cameron described the pollution as “extraordinary” and urged people to seek advice from the Met Office and Public Health England.
He said: “I didn’t go for my morning run this morning, I chose to do some work instead but you can feel it.”
In Wales, health officials have warned air pollution is predicted to be very high.
Parts of the north east of the country are expected to reach level eight – meaning high – around the Dee estuary.
People with lung and heart problems are advised to avoid strenuous activity outdoors, while those suffering symptoms of pollution – including sore eyes, coughs and sore throats – should cut down the amount they do outside, Defra said.
And Kay Boycott, chief executive of Asthma UK, said “the two-thirds of people with asthma who find that air pollution makes their asthma worse will be at an increased risk of an attack”.
“Asthma UK warns the 3.6 million people at increased risk to be sure they always have a working blue reliever inhaler on them and take their preventer inhalers as prescribed,” she said.
In February, the European Commission launched legal proceedings against the UK for failing to reduce levels of NO2 air pollution.