But the question of whether mobile radiation is a serious risk to our health still preys on our minds...One week after manufacturers were told they must display radiation levels on all new mobile phones, worrying research has revealed that the warming effects of mobile phones speed up brain function and in the long-term could increase the risk of users developing brain tumours. Dr Alan Preece, head of Biophysics at the Bristol Oncology Centre, said that radiation from mobile phones triggers a chemical process releasing stress proteins. Preece said that six separate studies have been carried out indicating that the response times of individuals exposed to radio frequency signals from mobile phones have sped-up. He warned this could have a "detrimental effect". But a spokesman for the National Radiology Protection Board (NRPB) disagreed saying: "Preece's comments represent biological effects only, which can be reproduced from other studies, which I see he has done, but it will be hard to prove whether these have a bearing in the long-term." While the NRPB spokesman admitted Preece's findings to be "a very interesting area of work". He said the industry had adhered to all the recommendations from the Stewart Report into the subject released last December. "Phones will start displaying radiation emission levels from 1 October after an EU system testing process was adopted," he said. However, not all phones will be labelled by this date. A spokesman from the Mobile Phone Manufactures' Forum admitted it hopes all mobiles will display their rates by 31 March 2002. The limit allowed is two watts per kilogram and the NRPB spokesman said none of the phones it has tested currently on the market have exceeded 1.3 watts. Vodafone, BT Cellnet, One2One, Orange and Virgin were unavailable for comment, while the Federation of Electronics Industry (FEI) authorised to speak on their behalf had no comment on the NRPB.