The debate over the planned expansion of Heathrow airport took another twist today with the revelation that the EU is concerned that the development of a third runway will lead to a significant breach of air pollution limits.

According to Guardian reports, the European Commissioner Stavros Dimas is to contact the UK government to voice his concern that the plans will result in the airport missing EU-imposed targets for nitrogen oxide targets.

The newspaper claims to have seen a letter from the Commissioner stating that he is to contact the UK authorities over the matter.

"Technical reports underpinning the Heathrow expansion suggest that nitrogen limit values near Heathrow will be significantly exceeded in 2010, the year in which those limit values become mandatory, and that this will be the case even after 2015," he said in the letter.

The development is a further blow to the proposed plans for a third runway, a final decision on which is to expected to be taken before the end of the year after the government has sifted through about 70,000 responses to its recent consultation.

The government maintains that pollution limits will not be breached " significantly", claiming that while it expects a small breach in 2015 as the airport switches to so-called "mixed-mode" flights that will see continuous take-off and landing from the two existing runways, this will be an interim measure ahead of the third runway being completed.

However, the news further highlights the contentious nature of the government's projections on pollution, carbon emissions and noise levels as a result of expansion.

Only last month a study by the Stockholm Environment Institute argued that the economic case for expansion was flawed and failed to take account of a potential slowdown in passenger numbers because of higher oil prices, expanded use of videoconferencing and improved rail services. Meanwhile, BAA came under fire for claiming that the development of "green super jumbos" would help limit the environmental impact of the expanded airport, despite there currently being no plans for such an aircraft to be built.

Earlier this year, the government-backed Environment Agency also raised concerns about the plans, arguing that the government had failed to adequately prove in the initial consultation document that the expansion would not lead to a breach of EU air pollution rules.