By Roger Pinney BBC Wales environment correspondent

How concerned should you be if you heard a communications mast was going to be erected near your home? Well, very according to groups springing up across Wales to oppose Tetra, the new police walkie-talkie system. Not at all say government experts. None the less from Snowdonia to the Gower, communities are campaigning to block the masts.

Tetra is a new hi-tech police secure communications system. Its in the process of being rolled out across England and Wales with the erection of 3,200 masts - 300 of them in Wales.

But, the project is facing mounting opposition on health grounds.

"What we want is guaranteed health now. Not compensation 30 years down the line." Kevin Jones sentiment is one commonly held in communities confronting what they believe to be a new and dangerous menace.

Kevin Jones manages the Cei Bach Country Club near New Quay on the West Wales Coast. Its near the village of Gilfachreda where O2 Airwave want to put up one of 300 Tetra masts planned for Wales.

When I wrote the Tetra report I said it must never be used and I haven't changed my mind Physicist Barrie Trower

"It came as a surprise to us," he says. "We had no chance to challenge the planning application and you can read on the internet that Tetra can cause cancer and all sorts of health problems."

That's a genuinely held fear not just in Gilfachreda but in a growing number of communities across the UK. They are united in attempting to oppose the spread of Tetra technology.

In Snowdonia at Beddgelert, locals have blocked the road to the proposed mast site. On Gower the opponents managed to force a public inquiry.

Tetra works much like a mobile phone, except that the operating frequency is close to that of human brain waves. Critics claim that poses all sort of health risks including cancer.

There's no evidence the signals from the masts can affect people. Tetra is new to this country. But its actually been used all over the world. NRPB's Dr Michael Clarke

Physicist Barrie Trower has researched Tetra for the Police Federation. His report was highly critical and he's sticking to his guns.

"When I wrote the Tetra report I said it must never be used and I haven't changed my mind," he says.

"Tetra is particularly dangerous because it modulates at 18 pulses a second , which is very close to natural brain rhythms and can affect those rhythms and hence our brains."

Clear enough? Well its not that straightforward. Supporters of Tetra, including the Home Office who are funding the programme, and the National Radiological Protection Board (NRPB) are equally emphatic - Barrie Trower has got it wrong.

"There's no evidence Tetra can be harmful," says Dr Michael Clarke, a scientist at the NRPB.

'Catch 22'

"There's no evidence the signals from the masts can affect people. Tetra is new to this country. But its actually been used all over the world. In Australia, in New Zealand, in Italy. Its actually used in the London underground, and its not affected people there."

The UK Government has responded to the health concerns by commissioning London's Imperial College to carry out a study. It will look at the affect of Tetra on police officers using the system but it wont report for a decade.

To the lay man, conflicting scientific advice then. And the promise of a report years down the line. All contributing to the worry says Kevin Jones back at Gilfachreda.

"We are in Catch 22 situation. What do we do?," he asks. "Do we sell and move on or do we stay and hope that nothing happens in the future."

The Home Office says Tetra should be fully operational by the middle of next year. The arguments over its safety will run on a lot longer that.