People are finding innovative ways to travel in London
Thousands of people have been unable to travel in London as snow disrupted the city's transport network.
Only limited bus routes were running in central London and Tube lines, including the suspended Circle line, coped with the effects of the weather.
London Mayor Boris Johnson suspended the city's congestion charge for the day and said authorities had done "pretty well" under the circumstances.
Both runways at Heathrow Airport were closed although one has since reopened.
London City Airport will remain closed for the rest of Monday and flights at Luton Airport will not resume until 2100 GMT.
The snow caused a Cyprus Airways flight to slip off a taxiway at Heathrow, leaving its front wheel stuck in grass.
Passengers were unhurt in the incident which took place at about 0820 GMT, airport operator BAA said.
The operator added it was the last flight to land before the runways were closed.
British Airways cancelled all flights until 1700 GMT.
A trickle of mainly long-haul flights has since begun to depart Heathrow, but many more are delayed or cancelled.
Passengers are strongly advised to check the BAA website's live departures board before setting out for the airport, a spokesman said.
Earlier, all bus services in the city were suspended. A few were gradually reintroduced but most remain withdrawn owing to slippery road conditions.
London has seen the heaviest snowfall in 18 years, weather experts said, with an accumulation of 20cm (8in) in some areas.
'Message to heaven'
Mr Johnson said: "I think we've done pretty well in what are absolutely extraordinary circumstances.
"There's no doubt about it, this is the right kind of snow, it's just the wrong kind of quantities.
"My message to the heavens is: 'You've put on a fantastic display of snow power but that is probably quite enough'."
By mid-morning, up to 10cm (4in) of snow had fallen in parts of Greater London, with 6cm (2in) of snow reported at Heathrow Airport.
Impact of the snowfall
Most London buses suspended
Circle line suspended
Reduced service on Southern and First Great Western
London City airport closed
One runway at Heathrow closed
Treacherous driving conditions
More than 260 schools closed
Heathrow Express suspended
Gatwick Express - 1 train an hour
Stansted Express - 2 trains an hour
The conditions led the Met Office to issue an extreme weather warning for London and the south east of England.
On the Underground, the Circle line is fully suspended, while Hammersmith & City trains are not continuing eastbound of Aldgate East station.
There are partial suspensions on the Central, Bakerloo, Jubilee, Piccadilly, Metropolitan and District lines.
There are minor delays on the Northern line and a good service reported on the Victoria and Waterloo & City lines. Several Tube stations are also closed.
Services are severely disrupted on Southeastern Trains and there is only one Gatwick Express train an hour. Southern and First Great Western are running reduced services.
The Heathrow Express trains are suspended and the Stansted Express trains are reduced to twice an hour.
Although Gatwick Airport was open, there were significant delays and cancellations.
Passengers were advised to check before leaving for the airport.
On the roads, the southern section of the M25 has treacherous driving conditions between the M23 and the A3.
The Highways Agency said there have been too many minor accidents on the roads "to put a number on" and recommended people should only take essential journeys.
A London Ambulance Service spokesman said it received more than 650 calls between midnight and Monday morning and stressed that it would only respond to "life-threatening calls" as it was under "severe pressure".
Most Tube services were severely disrupted
London NHS has advised patients who have outpatient appointments or are booked to undergo non-emergency surgeries to call their local hospitals before travelling.
Many elective procedures have been cancelled and out-patients clinics closed both Monday and into Tuesday.
More than 260 schools across London have been closed with the boroughs of Haringey and Camden in north London, Westminster in central London, Hounslow and Ealing in west London, Bromley and Lambeth in south London and Barking and Dagenham in the east being the worst affected.
Eurostar services from London are currently operating but are subject to possible delays.
Night-time temperatures across London could drop to -3C as a blast of cold air sweeps in from the North Sea.
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