Dense fog is causing travel disruption across London and Essex, as Defra has issued a warning over toxic air pollution.

The government department warned levels of air pollution are “very high” across much of the capital today (Monday, January 23).

The fog that descended over the region overnight has left dozens of flights cancelled at London City Airport, while more than 100 departures were cancelled at Heathrow.

The Met Office issued a severe weather warning for London, South East England and parts of South West England as dense fog hit the morning rush hour.

A yellow warning of fog was still in place until 10.30am, but freezing temperatures and low winds could see it persist into the afternoon.

Met Office forecaster, Mark Wilson, said: "Heathrow is currently on 100 metres' visibility, which is very dense fog, Gatwick is on 100 metres, London City Airport is on 100 metres and Stansted is on 100 metres.

"It looks like it will generally improve through the last part of the morning and into the afternoon, but one or two spots will hang on to fog for much of the rest of today."

Defra forecasts air pollution levels across London and Essex to remain in the high to moderate range for much of tomorrow.