• Snowfall of up to 15cm and temperatures down to -9C
• Met Office issues amber weather warning
• Heathrow cancels third of Sunday flights
Heavy snowfall is expected across much of Britain, prompting Heathrow to cancel around a third of Sunday's flights.
An amber weather warning – the second-highest level – was issued by the Met Office, with snowfalls of up to 15cm expected, along with daytime temperatures as low as -9C.
Heathrow announced a reduced flight schedule to "minimise the disruption to passengers" caused by ice, snow and freezing fog but said it anticipated more than 70% of passengers would still be able to travel as airlines would transfer them between flights. The revised timetable was due to appear on the airport's website at around 6pm and passengers were advised to contact their airline for more information.
Heathrow's chief operating officer, Normand Boivin, said: "This decision ensures that the greatest number of passengers can fly with the minimum amount of disruption."
Latest forecasts suggest snow will fall at Heathrow from 5pm on Saturday until 6am on Sunday, with the heaviest dump between 9pm and 3am.
Met Office forecaster Steve Randall said average snowfall would be 4-8cm (1.5-3.5in), including in London, but some easterly parts and high areas could expect 15cm.
"There is a band of rain moving eastwards and this will turn to snow and sleet," he said.
The rain, sleet and snow will be replaced by dry and frosty weather overnight with black ice expected to be an additional hazard in many areas. The north and west of England, together with Wales and western Scotland could expect rain instead of snow, and milder temperatures.
The amber weather alert applies to Yorkshire and Humber, the west Midlands, east Midlands, east and south-west England, as well as London and south-east England, and north-west England. A yellow alert, which warns people to "be aware", was in place for parts of Scotland, Wales and north-west England.
The deep freeze has seen daytime temperatures plummet four or five degrees lower than average for February – traditionally the coldest month of the year.
Overnight, temperatures fell to -12C in Benson, Oxfordshire.
The Department for Transport's salt stocks across Britain stood at more than 2.4m tonnes – a million more than last year.
The AA said it had been called out to more than 4,300 breakdowns so far this morning – around 1,500 an hour – and it expected this figure to reach up to 16,000 by the end of the day. This is almost double the 8,500 of a usual Saturday.
A spokesman said most breakdowns occurred because of flat batteries, which produce less power in low temperatures.
A Local Government Association spokesman said council staff and volunteers would be checking to see whether vulnerable people were being cared for, and people were being encouraged to call in on elderly neighbours.
"Motorists are being advised to check the latest weather and gritting updates on council websites and 'gritter Twitter' feeds, as well as refresh themselves on winter driving guidance and what to stock in their car," he said.
British Gas said it had received more than 200,000 calls in the last five days, compared with 120,000-140,000 during a normal winter week.
A string of sporting events have fallen victim to the icy conditions, with Portsmouth's home match against Hull City becoming the first Championship fixture cancelled due to a frozen pitch. Several matches in the lower leagues had already been called off.
Racing was heavily hit, with meetings at Ffos Las, Sandown and Wetherby cancelled. Sunday's meeting at Kempton will be subject to an inspection because of the threat of overnight snow.
But swimmers were not deterred by ice on the Serpentine in London's Hyde Park and gritted their teeth as they plunged into its chilly waters.