Living near high voltage electrical pylons substantially increases the risks of contracting cancer, according to a study by doctors at the University of Bristol Medical School, UK. The potential health effects of the electromagnetic fields generated by high voltage cables has been a highly controversial issue for more than 20 years. Studies in Sweden, Germany and New Zealand have indicated a possible link with cancer while similar studies in the UK, Norway, Canada and the USA have shown no evidence of any health risks. However, most studies so far have investigated the direct effects of electric and magnetic fields on the body. The size of the electric field is related to the voltage and the magnetic field to the strength of the electric current. Both diminish rapidly with increasing distance from the source and by about 100 m away are no longer measurable. Yet the unpublished by study by Dr Alan Preece of the university's oncology department, described on BBC radio on September 21, claims that electrical cables can have effects at up to 400 m distance. He has found evidence of a 29 per cent increase over the expected rate of lung cancers in people living near pylons in the south west of England. But the mortality only occurs in those people living downwind of the pylon. These findings provide support for a theory proposed by Professor Denis Henshaw of the department of physics at the same university. He believes that the fields cause changes in the properties of pollution particles in the atmosphere which increase the likelihood that they are deposited on the surface of the skin and lungs. However, the National Radiological Protection Board, the UK Government body established to monitor radiation risks, discounted the theory as 'implausible and highly speculative.' Meanwhile, Dr John Swanson, scientific advisor to the UK Electrical Association said that the industry has spent huge sums on investigations in to the health effects of power lines. 'When you look at the totality of studies, then you come to the conclusion that the balance of evidence is that power lines and the fields they produce do not have an effect on health.'