THE DEPARTMENT for Transport (DfT) has denied it plans to put the M4 in a tunnel at Heathrow to improve air quality.
Reports surfaced last month that the DfT was considering building 6km of tunnel between junctions 3 and 4a of the motorway and the airport spur, to mitigate the effects of a third runway at the airport.
A white paper published before Christmas recommended a third runway should be built by 2020 only if 'stringent environmental limits can be met'.
But in 2010, EU legislation will make it illegal for residents to be subjected to NO 2emissions of more than 40mg per m3 of ambient air. Pollution experts believe the third runway would expose 35,000 people around Heathrow to illegal levels.
A DfT spokeswoman said there were issues surrounding air quality at Heathrow but added it was normal procedure to weigh up different scenarios as a way of focusing on the issues.
She said the DfT had released a report, based on modelling work by consultant AEA Technology, as a supporting document to the aviation white paper. This included assessment of the M4 road tunnel fitted with industrial-strength air scrubbers.
The spokeswoman added: 'We don't have any plans to put the M4 in a tunnel, although we acknowledge there is much work to be done if the new runway is to meet environmental standards.'