Plans to extend the £2.5bn police radio network to other emergency services took a knock last week after Network News discovered that at least one of the project's customers may pull out.

Early trials of BT's Tetra equipment in Lancashire have shown that it can interfere with electronic devices, and there are fears that the ambulance service will not buy it in case it affects medical equipment.

The London Ambulance Service (LAS) is due to take the new radio system in four years, and said that it was watching the Lancashire trial with interest to see if equipment would suffer badly. "We will not take a radio system that may have any interference with our medical equipment," an LAS spokesperson confirmed.

Jeff Parris, general manager of BT's Airwave division, said that unless ambulance and fire services sign up, Airwave would "not be sufficiently profitable" to be worthwhile.

Network News revealed in December that Airwave might lose the fire service as a potential customer, when it uncovered the fact that Tetra handsets spark and cannot be used in explosive situations.

Police officers on the Lancashire trial found that their Tetra radios interfered with speed trap machines and breath-test equipment, giving alleged criminals a defence in court. The Police Information Technology Organisation (PITO) said that "revised stringent guidelines" had to be issued about switching off radios to avoid potential interference.

Jersey police warned the Home Office about Tetra interference problems two years ago. The Home Office admitted that it knew this when it signed up Tetra but said that "testing has to be looked at to show the degree of interference".

BT was reluctant to comment on LAS' concerns but said it was confident that interference issues could be resolved. It is said to be working with PITO, Lancashire police and radio manufacturer Motorola to continue research.

"The pilot will go ahead as planned and police will have operational guidelines to deal with interference," a BT spokesperson said.

First published in Network News