Companies across Europe are hoarding permits to produce greenhouse gas emissions worth hundreds of millions of pounds, the Guardian can reveal.
The surplus credits have been amassed from over-allocation of permits to pollute from the European emissions trading scheme, and by buying cheap credits from carbon-cutting projects in developing countries and holding on to their more expensive official EU allowances.
The saved permits can be used to meet future targets to cut the greenhouse gas emissions blamed for global warming and climate change without actually reducing pollution, or sold for a profit in the future.
Campaigners for tougher emissions reductions said the saved-up allowances discredited the argument of some industries that much deeper cuts in future would be "fatal" because they could no longer afford to compete against rivals outside the EU.
However, companies involved said the banked credits would help them pay to develop new emission-cutting technology, and to meet emissions targets until that became widely available.
Industry also warned it faced "death by a thousand cuts" as a result of the next phase of the scheme, from 2013 and 2020, and other costly environmental legislation planned by government. Business leaders accused the government of being prepared to sacrifice industry to enable other sectors such as aviation to keep polluting and meet the UK's carbon budgets.
One steelmaker told the Guardian: "Officials see us as acceptable collateral in the fight against climate change. If we don't make anything in this country any more, it means people could still fly to Tenerife once a year and the UK will keep within the carbon budget."
He said meeting targets would require vast amounts of steel to build windfarms, nuclear reactors and electric cars. This would have to be imported from more-polluting steelmakers outside Europe if the industry disappeared in the UK.
The Emissions Trading Scheme (ETS), the centrepiece of the EU's pledge to cut greenhouse gases, has already been criticised for giving many companies allowances to emit more emissions than they need, leaving little incentive to reduce pollution, and for lax regulation.
The latest concern about "banking" credits involves companies also buying cheap allowances from "offset" schemes which reduce emissions in other countries, often China and India, and using these to cover their emissions while keeping their official allowances - which are worth more because projects in other countries could in future be banned.
Analysis for the Guardian by campaign group Sandbag of the figures for 2008, the most recent available, looked at the extra allowances accrued by four big sectors: iron and steel, coke ovens, metal ore processing, and cement, which together have 800 installations covered by the trading scheme, and include big names like ArcelorMittal, Thyssenkrupp, Corus, Holcim and Cemex.
Sandbag calculated the four sectors received permits to emit 66m tonnes more carbon dioxide than they needed in 2008, partly because predicted growth did not happen and partly because of the recession towards the end of the year. In addition they bought cheap offsets for a further 18m tonnes plus, which would then free up more EU allowances. In total the surplus allowances would have been worth nearly €1.2bn (£1.1bn) in 2008, or just over €1.1bn at today's closing price of €12.99. Based on the forecast average price of €30 a tonne for the third phase of the ETS from 2013-2016 by analysts Point Carbon they would be worth more than double that in future.
If the companies stockpiled over-allocated surpluses for the whole of this phase of the ETS, from 2008-2012 they could be worth as much as €3.2bn at today's prices, said Sandbag. Any more credits released by buying offsets would be on top of that.
"If they [companies] want cashflow, which in the current climate they may, then they'll cash in the allowances," said Bryony Worthington, Sandbag's founder and director. "But if they are thinking long-term then they'll be thinking 'I should probably hold on to them and insulate myself for the future'."
ArcelorMittal, the world's biggest steel producer, has pledged to use profits to invest in future energy savings to reduce pollution, but there were no guarantees they or any other company would have to do this, said Worthington. "How do we police it, they could be using it for dividends or anything," she added.
Ian Rodgers, director of UK Steel, said: "The climate change agenda won't affect the amount of steel consumed, but it will determine where it's produced."
According to industry estimates, the third phase could cost heavy industry - including steelmakers such as Corus, the chemicals industry and the ceramics industry - €1bn a year.
Sandbag will tomorrow publish in-depth analysis for 2008, including the biggest buyers of offsets from developing countries, and a map linking every offset scheme with their European customers.