Protesting hauliers have handed a petition outside Downing Street as the government faces growing pressure over its planned road tax changes.
Fuel prices have risen above 120p a litre at the pumps, leading to dissatisfaction from lorry drivers angry with the government's 2p increase in fuel duty.
Hauliers want the introduction of an essential user rebate which would allow HGV drivers to claim back 25p of fuel duty. This would bring Britain down to the EU average, they say.
The convoy of lorries, led by drivers from Kent, slowly advanced into central London. Police had ordering the protestors to drive at at least 40 miles-per-hour but many disgruntled drivers drove slowly.
Protestors were prevented from reaching Whitehall. Hauliers nevertheless made it to Downing Street, where they presented a petition listing their demands.
A 60-mile convoy from Wales, from Cross Hands near Llanelli to the Senedd in Cardiff Bay, also participated.
Mike Presneil of Transaction 2007, who is helping to organise the London demonstration, said: "Fuel is rocketing. The government has the power to act but appears not to be listening. Hundreds of UK transport firms are being driven to the wall."
Protestors point out Britain is the only country which charges the same duty for both diesel and petrol.
Attention today may be on the 2p increase but the government also faces a worrying headache over its plans to tax "gas-guzzling vehicles".
Increases to the vehicle excise duty designed to punish environmentally unfriendly cars will affect seven in ten drivers in Britain, the Telegraph calculates, including many of the country's worse-off.
Over 30 Labour MPs have signed an early day motion calling on Alistair Darling to reverse the hike as a result.
Many are warning the looming row over the tax could become another damaging episode for the government, still struggling to recover from its U-turn over compensation for 10p income tax losers.
"There are 30 million motorists in the UK. Not all of them will be adversely affected - some of them will gain - but there will be millions of people adversely affected," junior minister Rob Marris warned.
Caroline Lucas, chief spokesperson for the Green party, accused Gordon Brown and Alistair Darling of "failing to understand the uses and mechanics of green taxation".
"Charging the most polluting vehicles with a flat tax will do nothing but enrage motorists and discredit the aim of green taxes, which is to change behaviour by actively rewarding more environmentally friendly behaviour," she said.
"The flat road tax on vehicle ownership takes no account of road usage, and provides no incentive or reward for making less polluting travel choices."