Gordon Brown managed to avoid another embarrassing Commons defeat on tax last night by holding out the hope for potential Labour rebels of relief for hard-pressed consumers in the autumn.

A Conservative attempt to amend the UK Government's Finance Bill and block controversial plans to increase car tax on the most polluting vehicles by up to £455 was defeated by 303 votes to 240 - a majority of 63.

The Commons debate came as more than 500 lorry drivers converged on London to protest against ministers' refusal to cut the price of fuel.

The Tories branded Chancellor Alistair Darling's Vehicle Excise Duty (VED) plans "unfair and ineffective" and claimed poorer families would be hit hardest by the change.

The proposals also deeply concern Labour back benchers, with almost 50 having signed a Commons motion, branding the changes "retro-spective" because they will apply to all cars registered since March 2001.

However, Angela Eagle, the Treasury Minister, dismissed the alternative Conservative proposal as "undesirable, unworkable and downright peculiar", arguing that multiple systems of VED would cause a "severe administrative headache" for the DVLA, the transport authority.

She told would-be Labour rebels that she had been listening "extremely closely" to their views and reassured them that ministers were examining ideas put forward to help hard-pressed motorists and hauliers.

"The government recognises the impact that high fuel prices are having on motorists at the moment and it understands the importance of addressing these," insisted Ms Eagle.

Yet, she made clear there were no "easy solutions" to the pressures caused by rising fuel prices.

Only 24 hours earlier, the UK Government avoided a rebellion over the 10p tax issue by telling would-be Labour rebels that it would produce "concrete proposals" to compensate the 1.1 million households still losing out from its abolition.

As with VED, the 10p tax issue is likely to be addressed in the Chancellor's pre-Budget report in November; potential Labour rebels are hoping for more financial relief for hard-pressed consumers. Ronnie Campbell, the Labour MP for Blyth Valley, called on Mr Brown to "pull his finger out".

During the Commons debate, Justine Greening for the Tories told MPs that her party did not have a problem with graduated VED linked to the level of pollution of cars.

However, she said: "What we do have a problem with is ineffective green taxation that is nothing to do with the environment and is everything about eco stealth taxes."

The Treasury's take from the rising costs of VED, she argued, would increase from £1.9bn in 2006 to £4.4bn by 2010 when the measures were fully implemented.

Yet, she stressed, annual vehicle emissions would be reduced by just 0.16m tonnes a year by 2020, a "fraction of 1% of total transport CO2 emissions".

The consequences of the VED change, due to start coming into effect from next year, would, Ms Greening explained, be "more dramatic" than the impact of the abolition of the 10p tax band has been so far.

In total, 2.3m people would see their car tax rise, she added.

Labour critics of the UK Government plans appeared willing to wait until the autumn for answers.

Richard Burden, a Birmingham MP, said ministers had got "some thinking to do" over the planned changes but insisted MPs should give Mr Darling time to look again at the measures over the coming months rather than have a "knee-jerk" reaction.

His colleague, Robert Marris, a Wolverhampton MP and another prominent Labour critic of the UK Government plans, added: "I hope he (Mr Darling) reconsiders carefully and is not in any way stampeded by some of the siren voices around us.

"This is a complex issue which needs to be looked at in the round."

An attempt by the SNP to create a fuel duty regulator to use windfall revenue from soaring pump prices to reduce future increases was heavily defeated, as was a Liberal Democrat call for a 5p a litre cut in duty for the more rural parts of Britain.