Londoners are being warned of high levels of air pollution after days of dense fog and light winds allowed harmful particles to build up across the capital.

Mayor Sadiq Khan has triggered a high air pollution alert for Tuesday following advice from forecasters at Imperial College London, with vulnerable residents particularly urged to take care.

The warning comes as the Met Office issues a separate yellow fog alert for large parts of England and Wales, with visibility expected to fall below 100 metres in some areas overnight.

Forecasters say dense fog and very light winds allowed pollution to accumulate over the weekend and linger into Monday morning, with smoke from Bonfire Night and Diwali fireworks, as well as wood burning, likely to have contributed.

A statement from the Mayor’s office adds: "High levels of particle pollution are forecast for Tuesday after dense fog and very light winds allowed pollution to build up over the weekend and linger into Monday morning.”

It is the fourth high air pollution alert issued in London this year.

The Mayor is encouraging Londoners to help reduce pollution by walking, cycling or using public transport where possible, avoiding unnecessary car journeys and refraining from burning wood or garden waste.

Information has also been shared with GPs and emergency departments across the capital to help them support vulnerable patients.

Warnings will be displayed across London's transport network, including Underground services and bus stop countdown signs, while schools and London boroughs will also be notified.

Some London boroughs are covered by the highest levels of pollution, according to air pollution maps provided by the Apple Weather app.

The City of Westminster, Wandsworth, Lambeth, Merton, Ealing, Brent, Tower Hamlets, Greenwich and Bexley are all rated 10, with most of the other boroughs being rated 8 or 6, including Croydon, Richmond upon Thames and Kensington and Chelsea.

North London has somewhat clearer air, according to the maps, with boroughs including Haringey and Enfield mainly being rated 2 or 4.

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 Met Office has issued a yellow weather warning from 6pm on Monday until 10am on Tuesday, as forecasters predict another night of thick fog stretching from Luton to Manchester.

Conditions should begin to improve on Tuesday morning as the fog gradually clears, but the respite could be short-lived, with colder, frosty weather on the way later in the week.

Met Office chief meteorologist Jason Kelly said persistent high pressure, light winds and clear skies had created ideal conditions for fog to form, while weak November sunshine had made it slow to lift.

“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,” he said.

Met Office meteorologist Aidan McGivern warned that already poor visibility on Monday would worsen overnight, with some areas facing visibility of less than 100 metres.

Freezing fog patches are also possible across central and southern Scotland, while temperatures across the northern half of the UK are expected to fall into the low single figures.

In some sheltered areas with clear skies, temperatures could plunge to between minus 3C and minus 5C.

A cold front bringing rain to the far north of Scotland will introduce colder air across much of the UK as the week progresses.

Mr McGivern said in the daily video forecast the poor visibility during Monday is “thickening overnight”.

He added: “It’s a cold night in the northern half of the UK, with temperatures widely in the low single figures, and in some sheltered spots where we get the clear skies, minus three to minus five celsius.

“Outbreaks of rain, meanwhile, turn up in the far north of Scotland. This is a cold front, which will introduce colder air through the week across many parts of the UK.

“But in the meantime, this weather front, an occluded system, is moving into the South and South West, and that’s going to lead to a wet start to the day (Tuesday) for the south-west of England, and that rain eventually pushing into the South and central part of Wales, other southern coastal counties of England.”

It comes after particularly foggy conditions caused disruptions at London's airports on Monday, with several flights from Heathrow and London City airports cancelled.