Britain's emissions of the greenhouse gas carbon dioxide are now higher than they were in 1990, the benchmark year used in government targets to tackle the pollution which is driving climate change.
A study by scientists at the Tyndall centre, at Manchester University, shows that soaring carbon emissions from the aviation and shipping industries have swamped attempts to reduce pollution from other UK sectors.
The analysis is the first attempt to measure total UK emissions by including those from all ships and aircraft - one of the fastest growing sources of greenhouse gases, yet not included in official data on emissions.
The news will give more ammunition to critics of the government's credibility on climate change amid mounting exasperation among scientists that politicians who acknowledge the threat of global warming are failing to take serious action to cut emissions.
Kevin Anderson, who led the study, said: "The atmosphere doesn't care where the carbon comes from, so in any rational approach you can't just conveniently forget to count some sectors."
Emissions from aircraft and ships entering and leaving Britain have more than doubled since 1990 and are expected to double again within a decade.
The study comes as ministers are poised to publish a review of climate change policies intended by 2010 to reduce carbon dioxide emissions by 20% on 1990 levels. But the scientists say such targets are misleading, because they do not include all sources of pollution.
Dr Anderson said: "Even if we were to meet that target, the level of carbon dioxide sent into the atmosphere could still go up because of this huge blind spot in the calculations. If aviation and shipping emissions are included, then the UK has not made any reduction in carbon dioxide emissions since 1990."
Official reports on carbon dioxide pollution do not include that from aircraft and ships using British airports and docks because it is classed as international. But Dr Anderson said to ignore this risked invalidating a government pledge to cut carbon pollution by 60% below 1990 levels by 2050, which scientists say is the only way to prevent dangerous climate change.
"If the government uses that 60% target as a basis for action then it has to say we're interested in emissions as a total from the UK," Dr Anderson said.
To include pollution from ships and aircraft, Dr Anderson and his colleague, Alice Bows, combined government statistics on carbon dioxide emissions, data on fuel use at UK airports, and figures on the number of ships using British ports.
With these forms of transport included, they calculated that UK carbon emissions in 1990 were between 171m and 175m tons. Emissions fell sharply in the early 1990s as Britain switched its power stations from coal to gas and closed down much heavy industry, but by 2004 had risen again to between 172m and 177m tons. Without shipping and aviation included, emissions fell by 4% over the same period, from 161m to 155m tons.
Elliot Morley, the minister for climate change, said: "We know that aviation emissions have risen and they've always been outside the calculation. But you've got to be careful that you don't use them as an excuse for not taking action in other areas." Shipping could join aviation in European schemes to curb pollution by trading emissions, he suggested.