Cycling groups have hit out at attempts to make helmet wearing compulsory - claiming it could reduce cycle use and the health benefits of the activity.
Cyclists don't want to be told to wear helmets
They claim making it illegal for under 16s to cycle without a helmet is likely to exacerbate the problem of obesity.
Eric Martlew MP hopes his Protective Headgear for Young Cyclists Bill will receive government backing.
The British Medical Association says it is in favour of cycle helmets but is against compulsion for health reasons.
The row over cycle helmets erupted after Labour MP Mr Martlew promoted his bill at a press launch in Westminster with the backing of Formula 1 ace David Coulthard.
The McLaren driver, a keen cyclist who has a company selling cycle helmets, insisted he would not get on his bike without wearing one.
Mr Martlew says he would like to see the use of helmets become as common as wearing a hat for horse-riding.
But his plans have angered a number of cycling groups, including CTC, the national cyclists' organisation, which says making helmet use compulsory would discourage people from taking to their bikes.
Roger Geffen, CTC's campaigns and policy manager, said: "If passed, this Bill would almost certainly undermine the efforts of government, local authorities, health professionals and others to achieve a trebling of cycle use by 2010.
"By reducing cycle use and exacerbating the trends towards car-dependent sedentary lifestyles, this Bill would almost certainly shorten thousands more lives than it could ever hope to save."
The organisation questions claims by supporters of the bill that head injuries account for more than 50% of all child cycling injuries.
Mr Geffen says CTC analysis of Department of Health data suggests that of child cyclists admitted to hospital in England in 2002/3, 37.6% had head injuries.
This compared with an equivalent figure of 43.7% for child pedestrians. Of all children's admissions to hospital in that year 34.2% had head injuries.
CTC argues that 15% of children aged between six and 15 were obese in 2001, numbers which are expected to rise to one fifth of boys and a third of girls by 2020.
While obesity shortens life expectancy by about nine years, cycling increases life expectancy by about two years, the group claims.
Philip Darnton, acting chair of the National Cycling Strategy Board, said the group was not anti-helmet wearing.
"We are opposed to mandatory helmet wearing, which apart from connotations of the nanny state, is quite unenforceable," he said.
"It would dramatically reduce the number of cyclists and be the worst possible step to take when we are also concerned about the desperate health problems arising from obesity."
Dr Vivienne Nathanson, head of science and ethics at the BMA, said it was "very much in favour of encouraging people to wear cycle helmets".
But the association was opposed to compulsory use at the moment because of fears it could "undermine" the aerobic and cardiac benefits" of cycling, she said.
"There is no doubt in our minds that cycle helmets make a significant contribution to safety, particularly in low speed impacts," she told BBC News Online.
But the BMA argues that compulsion could mean people abandoning cycling and exercise in general because of the cost of new equipment and other issues.
Dr Nathanson said advertising and education was needed to "make people understand" why they should wear helmets.
She urged designers to make helmets "look fun and funky" to encourage children to wear them, while including clear instructions on how to wear them properly.
The Royal Society for the Prevention of Accidents (Rospa) says it advocates the use of cycle helmets, but would only support compulsion if enough people were already wearing them to make the law enforceable.
Spokesman Roger Vincent said: "We need to persuade people of the benefits of wearing a helmet, with designs that are more attractive for children to wear."
The bill is backed by Dr Andrew Curran, a leading child neurologist at Alder Hey Hospital in Liverpool, who says wearing a cycle helmet reduces the risk of brain injury by 80%.