Britain was braced for the long-threatened big freeze today which was due to sweep across the country.

Temperatures plummeted as a cold front swept in from the North Pole, expected to bring with it heavy snow to most parts tomorrow, Wednesday and Thursday, according to forecasters.

The Arctic weather had been expected to arrive in Scotland yesterday, before taking an icy grip on the rest of the country this morning.

Temperatures did drop to well below zero in some northern areas overnight - with minus 6C recorded in Katesbridge, Northern Ireland, and minus 5C in Redesdale, Northumbria.

Seven inches of snow was reported just south of Inverness.

But forecasters said the freezing weather would not take full effect on most of the country until tomorrow.

Liz Anetts, from the PA WeatherCentre, said: ''Through tonight and Tuesday that cold air will continue to set in and it will be particularly cold through tomorrow and Wednesday.

''There is a risk of snow everywhere, with the heaviest snow showers likely to be in Scotland and north east England.''

She said temperatures would be between zero and three degrees during the day, before dropping to as low as minus seven at night.

Heavy snow is expected in Scotland, while even the south east of England is likely to get ''a few centimetres'', she added.

The Highways Agency had 700 gritters on 24-hour stand-by to ensure there was no repeat of last year's winter roads chaos, when much of the country ground to a halt in icy weather.

A spokeswoman for the Highways Agency said it was better prepared than ever for the wintry conditions.

''Everyone is on 24-hour stand-by and we are ready to go as soon as temperatures plummet,'' she said.

''The key thing is not to grit too early or grit too late - that is the lesson we learned last year. We are better prepared all round.''

She said the Highways Agency had refined its decision-making process to ensure the roads stayed clear through this winter's big freeze.

It now reviewed information about the weather more frequently and had better links with the Met Office, she said.

Householders have been warned that the cold snap could cause damage costing hundreds of millions of pounds due to frozen or burst pipes. British Gas is predicting that the plummeting temperatures could trigger more than 20,000 emergency calls a day.

AA Roadwatch warned drivers in snowy conditions to make sure their car is in good mechanical condition before setting out - and not to travel if the trip is unnecessary.

''In the event of snow. drive slowly, take care, and do not make unnecessary journeys,'' a spokesman said.

''If you are driving in an area where it might drift, take a spade. Make sure you have enough warm clothing, that your mobile phone is fully charged, and take a vacuum flask with a hot drink.''