Motoring organisations predict congestion on main routes into all large cities - particularly the outskirts of London.
The annual rush is expected to be heavier because the weather has become milder following the freezing fog and ice which caused havoc towards the end of last week.
Motorists returning after weekends away are also likely to add to the traffic congenstion - although the big rush home is expected to begin in earnest tomorrow.
An AA spokesman said last night: "We expect a lot of congestion on the urban roads as people head into the city centres looking for bargains.
"We expect the numbers moving across the country to increase steadily as the day goes on, but the majority of people coming back from weekends away will travel tomorrow.
"There are still a lot of road works up, so there will probably be a number of traffic jams on some roads."
The London Weather Centre said the cold weather would continue to be swept away by a warm front moving across the country.
The milder weather provided a let-off for bookmakers who faced a second year of big pay-outs to punters who bet on a white Christmas.