Getting back on the roads after the festive break is depressing enough but now motorists face two years of traffic misery due to major roadworks on the M25.

There are fears that tailbacks will stretch as far as Brighton as the cones were put out today to start a £147 million road-widening scheme on the busy London orbital road.

Transport officials have warned drivers not to try bypassing the roadworks by cutting through surrounding villages.

The motorway is being expanded to eight and ten lanes from junction 12 at the M3 interchange to junction 15, where traffic from the M4 joins the road.

The four existing lanes will remain open at peak times but will be narrowed, with a 40mph speed restriction imposed.

The measures could cause gridlock on what is one of the busiest stretches of road in Europe. However, many planners and drivers hope the scheme will improve conditions on the motorway, which has become notorious for its traffic jams and has been dubbed "Britain's largest car park".

A spokeswoman from the AA said commuters from Brighton using the M23 to London should prepare to find themselves caught up in major jams.

She said: "This could cause chaos. We really do not know what the impact will be at this stage.

"It's about 30 miles from the M23 to the M3 where the roadworks start but we all know what the M25 is like.

"It may take a few weeks to see what the impact will be - this really is a 'Who knows?' situation."

The work is being carried out by construction firm Balfour Beatty and overseen by the Highways Agency.

A Highways Agency spokeswoman said: "We are asking motorists not to try rat runs because it doesn't work and you're just clogging up local roads.

"With courteous and safe driving people should be able to get through the works in a reasonable amount of time.

"The reason we are doing this is because there is already congestion and we are hoping people will not notice that much traffic during the works.

"Motorists welcome the work but there is no gain without pain. Doing nothing was not an option."

There was less optimism from some Brighton drivers bracing themselves for major disruption.

Chairman of Brighton Streamline Taxis John Oram said: "This is going to be quite horrendous.

"Once the works cause tailbacks it will hit every intersection and we could have real problems where the M23 meets the M25.

"This puts our drivers in a difficult position as it means we cannot guarantee we will get a customer to their destination by a certain time."

Chris Donne, who owns Brighton-based road haulage company Midnight International 2000, said: "This is going to cause motorists some trouble.

"Going by the last roadworks like this at Reigate Hill, I think it's going to be catastrophic. Motorists should just stay at home.

"The more people who do not travel along that area of the M25, the better."

Brighton and Hove Green Party councillor Keith Taylor said: "Whoever thinks building ten lanes is going to satisfy demand is deluding themselves.

"Drivers going on to the M25 are going to have to endure total misery.

"I used to enjoy driving but now there is no pleasure in it and it's damaging the environment."

The work on the M25 will be split into four phases over the next two years.

The first stage is along the anti-clockwise, southbound section from junction 14 to 12.

Traffic-calming measures will build up over the coming week before the job of widening the motorway can start.

The Highways Agency and motoring organisations are advising drivers to leave more time to navigate the congestion and to keep to the new speed limits to avoid accidents.

The AA also suggests avoiding the roadworks where possible and to listen to traffic reports or use the internet to call up latest information about jams.

The widening programme should be complete by December next year and will also include a new route into Terminal Five at Heathrow airport.