By Richard Black
BBC environment correspondent
The UK's emissions of greenhouse gases rose between 2003 and 2004, according to provisional government data.
Transport is a growing emissions sector
The emissions last year were 1.5% above those in 2003, and are now higher than at any time since the Labour government came to power in 1997.
For the first time, the data also suggests Britain could miss its target set down under the Kyoto Protocol.
Opposition politicians and green groups have accused the government of losing control of greenhouse gases.
"The increase in carbon emissions and greenhouse gases shows the failure of Labour's strategy for tackling climate change," said Liberal Democrat shadow environment secretary Norman Baker, in a statement.
"The latest figures mean that we may actually miss our targets under the Kyoto Protocol."
The Kyoto treaty commits Britain to keeping annual greenhouse emissions during the period 2008-2012 to 12.5% below 1990 levels.
In 2002, the UK was 14.4% below 1990 levels, and in 2003, 13.4% below.
The provisional figures for 2004 show emissions are 12.6% below - just 0.1% underneath the Kyoto figure.
The government says the main reason for the increase is growing energy demand; statistics show that emissions rose from industry, transport and the domestic sector.
"The policy package they have isn't working," Bryony Worthington, climate change campaigner for Friends of the Earth UK, told the BBC News website.
"They need to make radical changes to it, a completely different approach, much more top-down management of emissions across the economy.
"If they don't do that, there's every sign that these trends will continue and we will miss our Kyoto targets."
Prime Minister Tony Blair and Environment Secretary Margaret Beckett have already admitted that Britain will not meet a unilateral target contained in Labour's 1997 election manifesto of reducing carbon dioxide emissions by 20% from1990 levels by 2010.
These latest government figures show CO2 emissions in 2004 were just 4.2% below 1990 levels.
'Not good enough'
Environment Minister Elliot Morley was pressed on Wednesday about Britain's record on meeting its international commitments at the launch of the Millennium Ecosystem Assessment, a comprehensive review of the state of the planet.
He acknowledged the UK needed to work harder to reduce its emissions but emphasised the progress the country had made compared with other nations.
"Whilst it's true there has been an increase in CO2 as a result of increased coal burn because of increased gas prices - in effect, since 1997, CO2 has been basically stable despite 17% [economic] growth," Mr Morley said.
"That's not good enough for us in this country - we have to do better than that - but it's a better record than any other industrial country globally."