The £2.9bn Airwave radio system designed to improve communications across the emergency services will require significant extra investment to meet its original objectives, according to experts involved with the project.

A Computing investigation has discovered that Airwave is struggling to deliver more than limited access to police computer systems, with concerns over its reliability.

We talked off the record to a wide range of people working on the project. Insiders claim that the number of radio masts need to double from 3,000 to 6,000, and that police will have to replace many existing handsets because changes in technology have rendered them obsolete.

Data transmission speeds currently vary between 3.2kbps and 7.2kps - far short of the 28.8kbs promised, restricting the use of planned functions such as accessing pictures and fingerprints.

Several police forces are already trialling GPRS-based systems to overcome the problems (Computing, 2 October).

'The thinking is that the cost of bandwidth will go down in the future so we will be able to use GPRS,' said one technician working on Airwave.

'At the moment though, to be able to do a lot of the things they were talking about, we will have to double the number of masts.'

Doubling the number of masts would involve a reworking of the whole network including switching and computers, according to an expert on police radio systems.

'Over Airwave, data can only travel half the distance of voice so to get a useful coverage for data they have to increase the number of masts. It's a law of physics and they can't get around it,' he said.

The Police IT Organisation (Pito) says the technology exists for Airwave terminals to handle data such as pictures when the service is available.

'Some of the older model terminals would need to be upgraded in order to display a picture on the handset,' said a Pito spokesman.

Jeff Parris, vice-president of the network's operator Airwave mmO2, says there is national debate over what services and data priorities will be needed.

'Data is the bit that is crucial to Airwave and it is up to each police force, fire brigade and ambulance trust to decide how to implement it,' he said.

Liberal Democrat Home Affairs spokesman Mark Oaten is to table a series of written questions in parliament over the effectiveness of Airwave.

'We want our police to have the very best equipment to help them in their fight against crime,' he said.