Freezing fog brought travel chaos to Britain this morning, with flights cancelled, roads jammed and severe delays on major rail services.
Heathrow cancelled between 60 and 70 flights due to the bad weather, while London City Airport was forced to cancel six flights.
The coldest spot in the UK last night was Tulloch Bridge in the Highlands where temperatures got as low as -10.2C (13F).
Other overnight cold spots included Chesham in Buckinghamshire at -9C (16F) and Little Rissington in Gloucestershire where it was -8C (18F).
Forecasters warn that although warmer weather is on its way, it will be accompanied by heavy rain.
The worst of the freezing fog lifted earlier this morning, with visibility steadily improving as the day goes on.
A Heathrow spokeswoman said: “There have been some delays as well as cancellations. There is bound to be a bit of a knock-on effect during the day. Also, some European airports are also affected by the cold weather.”
Cancelled flights at Heathrow included scheduled trips to Warsaw, Nice, Stockholm, Aberdeen and several German cities.
There was congestion on a number of major road routes, while a section of the A1(M) between junctions 39 and 40 in Yorkshire was closed.
On the railways, overhead wire problems caused 50-minute delays in the rush-hour between Bedford and Luton, while a broken-down train at Watford Junction in Hertfordshire also caused hold-ups.
An electrical supply problem led to delays to train services between Seaford and Lewes in East Sussex, while a signalling problem caused hold-ups to services in and out of another Sussex coastal station - Brighton.
In Scotland, a broken-down train at Bathgate led to delays between Edinburgh and Airdrie.
On the Tube, there were severe delays on the Metropolitan line between Rickmansworth and Amersham and minor delays on the rest of the line due to a lack of trains.
There were also severe delays between High Barnet and Finchley Central on the Northern line due to a signal failure at Woodside Park.
Another signal failure - at Arnos Grove in north London - led to delays on the Tube's Piccadilly line between Arnos Grove and Cockfosters.
“Some places where the fog lingers will struggle to get above freezing today,” said Matt Dobson, a senior forecaster with the Press Association's weather division, MeteoGroup.
He went on: “London and the South East, where the sun will eventually come through, may reach around 3-4C (37-39F).
”But in places such as the Vale of York and in the Scottish Glens it may stay as cold as minus 3C (27F) in daylight hours.“
Mr Dobson continued: ”This cold spell won't last. The fog will lift. But although the big change on Thursday night, with an Atlantic front moving in, will mean higher temperatures, there is likely to be a lot of wet weather.
“The south of England could be very wet on Friday and we are likely to see wet conditions all the way up to Christmas.
”The exception could be a short, cold snap in the weekend before Christmas.“
Train travel difficulties continued through the morning.
Overhead wire problems between Northampton and Rugby led to buses replacing trains between Northampton and Coventry, while an hourly train shuttle was running between Coventry and Birmingham New Street, with journey times in the area extended by up to 60 minutes.
There were also overhead wire problems affecting services in and out of London's King's Cross station.
The bad weather disrupted services at Christ's Hospital in Sussex, with trains between Barnham and Horsham delayed.
A broken-down train at Melton Mowbray in Leicestershire led to delays of up to 45 minutes between Leicester and Peterborough.