Londoners have been warned to expect high levels of air pollution after thick fog descended upon south-east England on Monday. 

Mayor of London Sadiq Khan placed the capital under an alert for high air pollution last night, urging ‘those most vulnerable’ to be wary.

Drivers are warned to switch off their engines when their car is stationary and homeowners have been told to avoid burning garden waste for risk of contributing to pollution levels. 

The warning came as the Met Office issued a yellow fog alert for much of England and Wales. It is forecasted that visibility levels could even drop below 100 metres. 

Dense fog and light winds, which first hit over the weekend, allowed pollution to accumulate into Monday morning. Smoke from Bonfire Night and Diwali fireworks are also likely to have contributed. 

Mr Khan wrote on Monday night: ‘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.’

Londoners have been warned to expect high levels of air pollution after thick dog descended upon south-east England on Monday

A train is seen travelling to Wimbledon, in south-west London, in dense fog yesterday

Visibility levels could drop below 100 metres as fog hits the cspital tomorrow

It comes after the foggy conditions caused disruptions at London’s airports, with several flights from Heathrow and London City airports cancelled yesterday morning.  

By 6.30am, seven flights from Heathrow and three from London City were called off.

Heathrow later advised anyone driving to the airport to allow extra time for their journey because ‘overnight fog had affected visibility on roads’ in the area.

‘We advise passengers to check with their airline before leaving home and to drive with care,’ it said on X.

Niamh Murray, Met Office operational meteorologist, said current weather conditions are the ‘perfect recipe’ for fog.

‘With autumn and winter and getting fog during this time of year, we get much longer nights, and that allows temperatures to fall away,’ she said.

‘We get a longer period of cooling and also the temperatures are much lower, so they’re much closer to the temperature that we need for the air to become saturated and therefore form fog.

‘Another thing that we need to form fog is quite light winds, not absolutely no winds.

‘We just have the perfect recipe at the moment: light winds, clear skies, long nights, to allow that fog to develop. And particularly if we see the negative numbers, it can be quite stubborn to clear the next day.’ 

The AA urged drivers to take extra care during the yellow warning. It said that motorists should reduce their speed, increase the distance between themselves and other cars and make sure their lights are switched on.

Vehicles are seen travelling on the M6 near Knutsford on Monday

It added automatic headlights shouldn’t be relied on – as they often can’t detect fog. Dipped headlights should be used instead, which will illuminate the back of the vehicle too.

The motoring association also reminded drivers to switch off their fog lights once visibility improved in the afternoon – warning that the bright lights could dazzle other road users.

AA president Edmund King previously said: ‘Fog can transform a familiar road in a matter of minutes, so drivers need to be prepared to adapt their speed and leave more room between themselves and the vehicle ahead.

‘One of the biggest mistakes is simply following the rear lights of the car in front. It can give you a false sense of security and means you may be travelling too close to react safely if that vehicle suddenly stops.

‘Ultimately, there’s no prize for arriving a few minutes early. Give yourself extra time, slow down and drive to what you can actually see ahead.’