ERRANT workers beware. Bosses worried about what their employees get up to outside the office can now ??spy?? on their every move by tracking them through their mobile phones.

The same technology ?? which is already raising Big Brother concerns among civil liberties groups ?? allows parents to keep an eye on their children when they go out or monitor the movements of elderly relatives to make sure they come to no harm.

The new service has even attracted interest from husbands and wives who suspect their spouses are cheating on them and want to know if they are seeing a lover while pretending to be elsewhere.

At least half a dozen firms are offering the tracking service, some for as little as ??5 a month. Controversially, it is based on information sold to them from the largest mobile phone networks, such as Vodafone, Orange and T-Mobile.

Networks and service providers are drawing up a self-regulatory code of practice and insist that only those who give their consent can be tracked. But critics fear that the technology might be open to abuse or, at the very least, will foster a culture of spying.

The tracking service relies on networks of mobile phone masts dotted around the country which normally receive and transmit signals to handsets within their vicinity. They can determine the location of a phone ?? and hence its owner ?? to within a 50m radius in towns and cities or within 2km in rural areas where phone masts are less densely spread.

To use the service, an employer or parent is initially required to register his own details and the number of the mobile phone he wishes to track on an internet website. A text message alert is then sent to the owner of the phone, seeking permission for it to be monitored in future. For employees issued with company phones this would merely be a formality.

Once permission has been granted, subscribers can locate these ??tagged?? phones at any time providing they are not switched off or run out of power. The owner would have no idea that his whereabouts had been checked.

Concerned parents, for example, could log on to a service provider??s internet site and find out which street their child is on at that precise moment. The technology could also be adapted to warn people when the owner moves out of one pre-defined area into another.

However, snooping on a cheating spouse without getting their consent first would not be so easy. A devious wife could sign up her husband??s phone to the tracking service behind his back, but she would soon be rumbled because messages warning the owner that the phone has been registered for monitoring continue to be sent at regular intervals.

??We get lots of inquiries along the lines of ??I want to put my husband on the system but I don??t want him to know about it??,?? said Andrew Overton, managing director of VeriLocation, a mobile phone tracking firm. ??But we have to say, ??Sorry, we can??t help.??

??Everybody??s worst case scenario is that this turns into an internet chatroom and gets used by paedophiles, but there are a number of things you can do to prevent that.??

Although he admitted no new technology is foolproof, he claimed that as many safeguards as possible had been put in place to prevent the service being abused. Subscribers have to be over 18, they have to provide an address, which is verified, and anyone trying to register a child??s mobile phone for tracking has to prove that they are a parent or a legal guardian.

Vodafone denied that it was acting irresponsibly by selling on location information to tracking firms, claiming that the firms had to meet rigorous standards and be acting within the Data Protection Act.

Mark Littlewood, campaigns director at Liberty, said: ??The mere existence of this technology will encourage a culture of spying.?? Pointing out the potential strain it could put on personal relationships, he added: ??If my wife asked me if it??s okay to track my phone, what am I supposed to say???

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