Protesting lorry drivers today created "horrendous" conditions on Britain's busiest road by crawling in convoy around the M25 London orbital route.
Huge 12-mile long tailbacks built up as truckers slowed to just 15mph in their protest against fuel and road tax rises.
New Transport Minister Helen Liddell condemned the demonstration but hauliers said they were fighting for their livelihoods.
Truckers were expected to park for the night at South Mimms in Hertfordshire and Clacket Lane in Surrey - the two M25 service areas from where the 48-hour protest began at lunchtime today.
It was thought that some hauliers could head for central London to stage a demonstration as close to the Houses of Parliament as possible.
Problems began on the 119-mile M25 almost as soon as the convoys moved off from the two service areas.
Within two hours, traffic on the western part of the orbital road was almost at a standstill as lorries occupied two and sometimes three lanes of the motorway.
"Conditions on some parts of the M25 have been horrendous, particularly between junctions 12 and 16 around Heathrow airport," said an RAC spokesman.
Kent-based haulier Frank Stears, who had helped organise earlier protests this year, said the demonstration had been "good natured".
He went on: "We have had motorists sounding their horns in support and we have not seen anyone getting aggressive. I think the protest has been a big success."
Mrs Liddell said it was "unfortunate that truckers are causing disruption".
She added: "I don't think it helps anyone and disrupts the lives of ordinary people trying to go about their daily business."
One of the protesters who moved off from South Mimms was Gary Donaldson, 54, who runs a small haulage business in Finedon, near Wellingborough in Northamptonshire.
He said: "The protest has had the desired effect. I know the public will be inconvenienced but how else can we get our argument across?"
The M25 action comes after protests on Monday in Middlesbrough, a demonstration in Newcastle last Saturday and other nationwide city centre protests in the past few weeks.
Hauliers are angry at recent price increases in the Budget and some fear they could go out of business.
Others have threatened to base their businesses abroad to take advantage of less stringent tax regimes. The Government has set up a road haulage industry forum to deal with truckers' grievances. But some hauliers say it is a mere "talking shop".
Mrs Liddell will inherit the chairmanship of the forum from her predecessor John Reid, who has become the new Scottish Secretary.
Two organisations which support the forum - the Freight Transport Association and the Road Haulage Association - said Mrs Liddell should meet industry leaders as "a matter of urgency".
