Should you be passing through the centre of Glastonbury and need to use your mobile phone, have a look at St John's church. High on the walls have been placed four microwave transmitters that beam out low-level radiation 24 hours a day. They are the object of deep suspicion and considerable fear.

While the vicar and the parish council were happy enough with the modern manna from heaven - mobile phone company Orange is paying several thousand pounds a year for the site - the locals are deeply upset. A petition of 2,000 signatures collected by a hastily formed group called Glastonbury Residents Oppose Microwave Masts in Town (Grommit) was turned down by the local authorities and appeals to the company and Downing Street were ignored.

It's a similar story at Bedonwel junior school in Belvedere, Kent. There a group of parents have been refusing to allow their children to go to school because they say radiation from the mast in the school grounds could be damaging.

The Glastonbury and Belvedere residents are echoed by communities in Somerset, Yorkshire, Surrey, Lancashire and Scotland. They have been joined by pressure groups as diverse as Friends of the Earth, the Council for the Protection of Rural England, the Country Landowners Association, ramblers, mountaineers and hillwalkers, all of whom have been fighting to stop masts being erected on top of hospitals, council flats and in areas of outstanding natural beauty.

And at last it seems they have not been complaining in vain. Yesterday an environment committee of the Scottish parliament recommended that all telecoms masts, including those for mobile phones, should be required to apply for planning permission, and that local authorities should adopt the "precautionary principle", keeping masts away from schools, hospitals and residential areas. If this passes into law, it will be the first brake on the breathtaking mobile phone revolution, which has seen 25m Britons buy handsets in just a few years. The backlash has started in earnest.

Nobody knows - or at least the companies, the government, local councils, Oftel and the Federation of Electronic Industries are unwilling or unable to say - quite how many masts and relay stations there are. Given that Orange, one of the four licensed providers, has said that it should have erected 10,000 masts by the end of the year and the three other operators - BT Cellnet, One 2 One and Vodafone - claim roughly equal coverage of Britain, there could be more than 35,000.

But we are only on the the edge of the new telecommunications forest. Within a few years there will be tens of thousands more masts. The exact number depends on how many of us turn to cellular phones and for what reason. Because each mast can, for the moment, only handle a few hundred calls at any given time, the existing infrastructure is beginning to prove inadequate.

Within two years, the companies expect there to be 40m mobile phones in use; within eight years not only do they expect just about everyone in the country to have one, they expect us to be well into the third generation of phones. This is the universal mobile telephone system (UMTS), which will allow people to send huge amounts of data and pictures to their mobile phones via the internet. To guarantee good connections, this system will need vastly more masts and relay stations.

But the telecommunications forest will spread further. The police and the emergency services are now linking with corporations to build a major system of their own, and a fifth major operator will shortly be given a licence. Each is expected to build thousands more masts.

The prize for the telecoms winners is huge. The hype has it that within 10 years cellular technology will handle almost 90% of all the telephone calls and data transmission at present travelling by landline. In the cities, it will mean masts, satellite dish transmitters and relay stations positioned every few hundred yards, mainly on buildings. Most will be relatively unobtrusive - often no more than small dishes or boxes attached to lamp-posts. The companies will try to expand the existing masts by tagging on new pieces of equipment, but very many will be brand new. In the country, depending on the terrain, the freestanding masts may in future have to be placed every few miles.

Hundreds of communities will have to increase their efforts if they want to stave off an invasion. "Opposing masts is hard," says Alison Tisdall, who with other Wiltshire residents objected strongly to a Vodafone mast planned just a few hundred metres from houses. "You cannot object on health and safety grounds; the government only accepts arguments about the thermal effects, which are impossible to prove". In the end, Vodafone withdrew its application when it was found that the council did not own the site of the planned mast. However, now there are other applications - to extend existing masts - being advanced by other companies.

The objections are not solely on health grounds. "We fought and fought," says Grace Jones, who, with other, opposed construction of a mast on the edge of the Peak District. "It was like punching air. The company was not interested in our concerns. They did not consult us. We felt utterly powerless to stop them spoiling a wonderful view."

Meanwhile in Guildford, Surrey, more than 15 masts have been erected since 1993 and at least 40 more in outlying areas. It is deeply frustrating for councillors, who in most cases have no way of controlling where masts are built and cannot persuade the companies to share masts. Nigel Sutclife, a borough councillor, has watched helplessly as up to six companies have each built their own mast in the same area, mostly bypassing the planning system. "If the previous government had required companies to cooperate, then we would have had a good network with a third or fewer of the masts, making huge savings in cost and environmental damage," he says.

But pressure is growing for government to review its guidelines, which say that councils should not question the need for a service or try to prevent competition between companies. In the next few weeks a report similar to that given to the Scottish parliament yesterday should go to the Department of Trade and Industry. It follows an early day motion, so far signed by more than 150 MPs, calling for precaution and more control. The local government association representing 150 local authorities throughout England and Wales has strongly criticised central government policy and also come down heavily in favour of banning masts from schools, hospitals and residential areas.

Many of the masts that are already in place may now be under threat. Earlier this month, a government planning inspector from the Department of the Environment, Transport and the Regions ruled that a much disputed Vodafone mast in Leeds had breached planning laws because the company, in calculating its maximum height, had not included the plinth on which the mast stands. The company has been given six weeks to remove the mast or lodge an appeal in the high court.

The companies - eager to present the best case before the new licensing round - admit mistakes have been made in siting some masts, but claim that they are now acting responsibly and consulting more widely. In fact they are learning where they will attract the least opposition. Considerable rents have been offered and accepted and more than 500 cash-strapped schools and dozens of hospitals and council flats now sprout tall masts. One Scottish council is believed to receive more than £800,000 a year from its masts.

But equally, many other councils are now objecting strongly on health grounds and, to the despair of the companies, are banning masts from all council properties. Over a third of all local planning authorities in Scotland and a growing number in England have adopted the precautionary principle.

The companies know their masts are eyesores and that the debate on the health effects is growing. They are, superficially at least, trying to address the problems. In place of the old gridiron constructions, which are the most unpopular, they are turning to tall, slim models and sponsoring designs that disguise masts as trees, lamp-posts, art works and flagpoles.

"We are as sympathetic to the environment as possible", says an Orange spokesman. "Our preference is always to use existing structures and to share masts. But sometimes we cannot. We only ever build a new site where no viable alternative exists."

The future may be Orange, but it's not at all clear how communities will react when the full network of masts is rolled out and further research is done on the health effects. In Ireland, they haven't waited to find out. There have been major demonstrations and several communities have pulled down the masts in the dead of night.

"Here in Glengarrif, County Cork, they put up a mast near the school," says Denise Hall. "The next thing, it was down. Nobody will say how it happened but the company never raised it again. There has been grave concern all over Ireland about the health and environmental impacts, and especially because the companies don't need permission to put them up. People have taken matters into their own hands."

The message for Labour, which has made new technology such as the internet and mobile phones central to its vision of future Britain, is clear. Having encouraged the telecom industry to expand like wildfire, it now needs to listen to the grassroots opposition. Only tighter planning controls and increased awareness of health concerns will avoid trouble spreading.

Radiation nation: the case against transmitters

Two years ago Orange installed a mobile phone base station and mast 70m from Jane Palmer's home in south Wales. Not long afterwards, her daughter Nicola, who had been diagnosed epileptic at birth and had been having one or two fits a month, began to experience four or five fits a day. Yet when Nicola is away from home, or the transmitter is turned off, Palmer says her daughter experiences hardly any problems at all.

Is this a coincidence or evidence of something very serious? The government, the National Radiological Protection Board which advises it and the mobile phone network operators insist that phone masts are operating well within safety guidelines. Technically, they are correct.

During use, a mobile phone and the transmitter mast emit microwaves, the same form of electromagnetic radiation as is produced by a microwave oven. The thermal, or heating, effects of these microwaves - which are present all around us from televisions, computers, wiring and stereos - have been studied for years and it has been found consistently that they have no great effect on people.

However, the radiation's non-thermal effects are being studied increasingly and this is where most of the concerns lie. There is a growing body of international scientific evidence suggesting that there may be serious health implications arising from long-term exposure to very low levels of microwave radiation - the sort Palmer would argue has been affecting her daughter.

Research in the US and elsewhere has found that electromagnetic fields and exposure to these frequencies may interfere with brain signals, leading to problems with the immune and nervous systems, and slower response times.

The NRPB does not recognise the scientific merit of these studies as they have failed to prove a categorical link between long-term exposure to low levels of radiation and ill health. The problem is that categorical proof is almost impossible to come by.

However, many countries, such as New Zealand and Sweden - and now Scotland - as well as local councils are choosing to apply a precautionary principle, especially when it comes to children, the ill and old people, who are believed to be more susceptible to low-level radiation. Britain has chosen some of the lowest safety standards in the world but amid widespread calls on the government for further study of the effects, the department of health is expected to report back to MPs later this year.