A terrible train crash. Desperate callers are trying to get through to the helpline number given out to see if their relatives are among the dead or injured. But the local police are so busy with the rescue operation that they cannot spare the time or the manpower to handle telephone calls, making an already terrible situation even more stressful for anxious relatives waiting for news.

This is how it used to be when the country's 52 police forces operated completely independently of each other. A force faced with a disaster on its patch did not have the technological backup to share the task of handling calls with neighbouring forces.

Now they do. The capacity to re-route helpline calls to another force when resources are stretched is just one of the ways the police service is harnessing new technology to make its operations quicker and more efficient.

The past five years have seen massive changes in the way individual forces communicate with each other and access centrally held information. The core of the system is the Criminal Justice Extranet, or CJX, hosted by Cable and Wireless, and first rolled out in 1999.

Unlike previous police computer systems, the CJX allows forces to link up to each other as well as to central databases like the police national computer, which holds records on criminals, stolen vehicles and property and the violent and sex offender register (ViSOR). Police can communicate over secure links with other parts of the criminal justice system connected to the CJX, including the Crown Prosecution Service, the Criminal Records Bureau and the Forensic Science Service.

Through the Extranet, officers can go online from their desks, log into databases and exchange e-mails over a secure connection. Systems use Windows-based software, which is already familiar to most officers and which means they need minimal training. And the technology is central and standardised, instead of being local and piecemeal.

Mick Humphrey, CJX liaison officer at the Police Information Technology Organisation (PITO) says: "Ten years ago police forces were local. Each police force had its own internal network infrastructure. Different forces spent money on different things. No two forces' uniforms or cars were the same, they had different mobiles, radios, catering arrangements. The network reflected this local nature."

Spending money on updating computer networks did not have the same populist appeal as putting more officers on the beat, admits Mr Humphrey. "But you can't do anything if you don't have the infrastructure. We needed all forces to be physically connected to each other and other agencies and we needed to persuade all forces to link up."

Now the Extranet is well established, with the help of government funding, and has 250,000 users across all UK forces. At the end of last year, Cable & Wireless signed a two-year extension deal with PITO, the public body responsible for providing IT systems to the police and other UK criminal justice organisations.

The Extranet has just been extended to allow officers out on the beat to log on remotely from a laptop or mobile, using the latest wireless broadband and 3G mobile phone technology. C & W is now investing £1 million to develop and upgrade the CJX network to provide facilities like video conferencing and digital imaging, which are, says Mr Humphrey "very band width-hungry" and require faster computer speeds.

Police forces are still locally funded and make independent decisions about how they structure their operations. But the networks are there for them to link into. "What we're trying to provide are centrally provided and accredited systems and services," he says.