The current weather conditions have led to a significant rise in smog levels around London. Parts of east London have been recorded at 'very high'.
Take a look at the figures in full from Defra here.
Flying high above London's fog today was the Met Police helicopter. The team on board took these stunning pictures of Docklands, and The O2 which is only just about visible.
Those who thought the last image was Canary Wharf are wrong (it looks like this...) http://t.co/i7u7x0BIkp
Recognition training for you today...stunning weather conditions, where is this? http://t.co/MiUkglY5kx
Thick fog has caused delays for thousands air passengers. Poor visibility led to 40 flights being cancelled at Heathrow airport. At London City Airport in Docklands nearly every early-morning service was either delayed or cancelled.
Major airports reported that they were back to "business as usual" after an air traffic control centre glitch caused chaos across the UK and Ireland.
Hundreds of flights were cancelled or delayed yesterday after problems arose at the National Air Traffic Service centre in Hampshire.
A spokeswoman for Heathrow Airport said: "Today we have 18 cancellations - 11 arrivals and seven departures - and that's mostly due to crew displacement. Apart from that we are pretty much running as normal."
A Stansted Airport spokesman said they had experienced no problems today, while a Gatwick Airport spokeswoman said: "We've been back to business as usual from this morning."
Thousands of passengers have been left stranded at all of London's airports after an unprecedented technical glitch.
Hundreds of flights have been cancelled or delayed and, as Luke Hanrahan reports, the knock-on effect means the problems could continue long into this evening.