A light dusting of snow across London today was enough to ground flights, cripple eight Tube lines and disrupt six rail networks.
The city woke up to about two centimetres of snow covering roof tops, parked cars and roads.
Eight of the 12 Tube lines were crippled, mostly due to the poor weather, a London Underground (LU) spokesman said.
When asked if the Tube maintenance firm Metronet had done enough to prepare open tracks for the freezing conditions, he answered: "They did not. Full stop."
LU had warned the firm to run de-icing trains and have extra technical staff available, he said. "The majority of the disruption could have been prevented if they had done the work."
But Metronet said it "strongly refuted" the allegations. It was LU that underestimated the severe weather risk as "small", a company spokesman said.
Metronet had raised the level to "risk" on the north and west of the Tube network. "We ran de-icing trains all night and abandoned all engineering work - other than essential track inspections."
The firm's spokesman added that most of this morning's failures were due to frozen signalling points, not iced conductor rails. Although points heaters are checked every six weeks, tonight all the points heaters would be checked again manually, he said.
This morning, four lines were suspended - all maintained by Metronet:
- the whole East London line, due to multiple signal failures on the partly open track;
- the Circle line, clockwise only, due to an earlier signal failure;
- the Metropolitan line between Amersham and Rickmansworth due to a faulty train at Chorley Wood; and
- the Bakerloo line between Elephant & Castle and Paddington, due to a fire alert.
The Central and Jubilee lines suffered "severe delays" due to signal failures at Hainault and Neasden respectively.
Minor delays plagued the Piccadilly line and the District line between Earls Court and Wimbledon, where trains run in the open.
Frozen signalling points caused travel chaos in London's railway network.
On Southeastern railways, a broken down train in Bickley, Kent, and the knock-on effect of multiple small problems caused delays of up to an hour across the firm's whole network. Buses have replaced trains between Tonbridge and Hastings.
South West Trains (SWT) reported 15 points failures at some of its busiest hubs. The company blamed problems at Waterloo, Clapham Junction and Wimbledon, as well as St Margaret's and Guildford, Surrey, on "sudden wintery weather conditions".
Southern trains reported disrupted services to Victoria from Portsmouth, East Grinstead and London Bridge.
On One Railway, signalling problems at Stratford hampered trains to Liverpool Street from Southend, Colchester and Norwich.
The weather also delayed all Thameslink services on First Capital Connect by up to 30 minutes, and disrupted Silverlink services between Euston and Northampton.
"We are working as hard and fast as we can to fix it," a Network Rail spokeswoman said.
By noon, British Airways had cancelled 31 short-haul flights from London airports.
Heathrow was worst hit with 21 cancellations, with a further 10 at Gatwick, a BA spokesman said.
"We do not expect further cancellations, as the runways have now been cleared from snow and ice."
On the M25, three accidents took place near Croydon, Surrey and Enfield respectively. "It was mostly down to people sticking to driving 60mph to 70mph when it is snowing," a Highways Agency spokesman said.
A lorry jack-knifed near Reigate, Surrey, closing three lanes between junctions eight and nine for much of the morning. No-one was injured in any of the accidents.
Last night the Highway's Agency sent out more than 100 gritters, of its total fleet of 400, to clear roads in the south and east.
In East and West Sussex, motorists were being urged to drive only if essential. Sussex Police received 74 weather-related calls this morning, including a car careering into a gas main in Buxted High Street.
Up to 5cm in places
Forecasters said more snow could fall this afternoon, but was unlikely to settle.
"We have seen the worst of it," said Met office spokesman Jon Hammond.
"There was a light covering of one to two centimetres of snow across London and the South East.
"Towards the west of the city, at Heathrow and in the Chiltern hills, it was as much as five centimetres in places.
In recent decades snow in London has "become a bit more of a novelty", Mr Hammond added. The last light dusting was in January 2004.
By midday, the showers had headed south across the Channel into northern France,
Tonight and tomorrow there will be further wintry showers of rain, sleet and wet snow, with temperatures dipping below freezing.
The weather should improve towards the weekend as milder temperatures of seven to eight degrees is expected to return.
Big Brother excitement
At the Celebrity Big Brother house in Elstree, north London, the light sprinkling of snow in the garden was enough to make several housemates ecstatic.
"Oh my god, my wish has come true," beamed singer Jermaine Jackson when he peered outside.
"Snow! Snow!" shrieked Shilpa Shetty as she ran into the house with a bowl of sludgy ice.
The Bollywood star explained that she had seen snow before, but never while it was still falling.
"Shilpa's so excited about the snow, (she) nearly laid an egg," comedy actres Cleo Rocos commented.
Nevertheless, Rocos pleaded: "Oh come on, snow some more - that would be so good. It would be like having a TV."