Labour Party MPs also put pressure on Prime Minister Gordon Brown to rethink planned fuel and road tax increases, prompting ministers to hint at a possible about-turn.
Drivers from across Britain converged on the capital in convoy, closing a busy artery and causing traffic backlogs. Similar protests took place in Wales, in a new headache for Brown whose leadership is under fire.
The drivers said fuel bills had risen by almost half in a year and demanded a rebate. French truckers threatened similar action.
Ministers, anxious after voters punished Labour in recent local elections, said they were listening to concerns.
There was no sign Brown would give in to the truck drivers but ministers said they would keep an "open mind" on a planned hike in vehicle excise duty that will hit families squeezed by rising fuel and food costs.
"We've made it clear we'll go ahead with the announcement we've made but we've also made it clear, and this is not contradictory, that we have an open mind in the future," environment minister Phil Woolas told BBC Television.
Woolas said a proposed two pence per litre rise in fuel tax, already postponed by six months to October, would be reviewed again in October as planned.
Justice Secretary Jack Straw earlier hinted at a possible policy change, telling BBC Radio: "The chancellor and the prime minister say they are listening to public concerns and if there are going to be decisions, they could be made in the autumn."
Newspapers confidently forecast a government "U-turn" on the vehicle tax.
The truckers argued they were essential to keeping the nation moving and that many businesses were at risk of closure.
"If we don't work the country doesn't work. It is only a matter of a few days before things grind to a halt," said Stephen Taylor, head of warehousing and distribution firm TM Logistics, who estimated that around 85 percent of goods were carried by road around the country.
"It is really bad, it is affecting all of us," Joe Cook, a truckers' spokesman, said, adding his weekly fuel costs had risen by more than 3,000 pounds since January.
PROTEST STARTS IN FRANCE
More than 200 trucks parked on a main thoroughfare leading into central London, police said.
Diesel is about 130 pence a litre, more than double the price in the United States. Hauliers want a cut in fuel duty of 20 to 25 pence a litre.
Britain levies the highest fuel duty in the European Union with nearly 65 percent of the pump price of petrol due to tax.
Welsh hauliers threatened to blockade ports and refineries if the government failed to come to their aid, stirring memories of refinery blockades in 2000 that brought Britain to a standstill. Prices then hit one pound a litre.
As in 2000, the fuel protests began in France, where fishermen have blockaded ports to demand cheaper fuel.
French truckers threatened to take action across France if the government failed to respond to their demands by Thursday evening. The truckers have demanded that industry diesel prices fall back to average levels seen in January this year.
Action taken would initially be localised but would "intensify into a hard conflict" if the government turned a blind eye to demands, truckers group OTRE said in a statement.
President Nicolas Sarkozy suggested using extra revenues from petrol taxes to help sectors affected by high fuel costs.
"It is always the same old promises. We will judge the facts. We want concrete (action)," said Yannick Pourchaux, president of the fishing committee of Fecamp in northern France.
