A high air pollution alert has been issued for London as a result of dense fog, as forecasters warn of transport delays and difficult travel conditions.
The Met Office earlier issued a yellow fog warning for parts of England and Wales, with visibility reduced to less than 100m in some places overnight.
Government monitoring recorded the South East and East Midlands as having “high” pollution, with Greater London recorded as “very high”.
Smoke from Bonfire Night and Diwali fireworks is also “likely to have contributed”.
In a post on social media, mayor Lord Sadiq Khan said: “I’m triggering a high air pollution alert for London on Tuesday 10 November.
“I urge everyone in the capital, especially those most vulnerable, to stay safe and follow health advice to minimise their exposure.
“Please switch off engines when idling and avoid burning garden waste, which contributes to pollution.”
Forecasters at Imperial College London advised Lord Khan to trigger the alert “after dense fog and very light winds allowed pollution to build up over the weekend, and linger into Monday morning”, according to the mayor’s office.
The deputy mayor for environment and energy, Mete Coban said: “Toxic air is responsible for thousands of premature deaths in London each year, which is why the Mayor has done everything in his power to tackle it, which includes launching the world’s largest clean air zone.
“It is really important we all do our bit to protect those who are most vulnerable as we continue working to build a safer and greener London for all.”
The alert is the fourth issued in the capital this year, with the last one made in June during a heatwave.
A yellow fog warning is in place until 10am on Tuesday, with the Met Office forecasting a “night of dense fog”.
The affected area stretches from Luton to Manchester, covering parts of central and northern England and Wales.
The fog is expected to develop across the warning area on Monday evening and will become dense at times overnight – with visibility reduced to less than 100m, according to the forecaster.
It will thin and clear during Tuesday morning, but will give way to cooler and frosty weather later in the week.
Met Office chief meteorologist Jason Kelly said: “Persistent high pressure has brought light winds and clear skies, allowing fog to form, while weak November sunshine has meant it is fairly slow to clear.
“We’re expecting one more night of dense fog, with a warning in place for some areas. Increasing cloud and wind should then limit further widespread fog from developing.”
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