Millions of people will be able to track each and every move by friends and family through their mobile phones, thanks to a new feature launched by Google yesterday.

The new system dubbed “Latitude” uses a digital map to show automatically exactly where a loved one is at any time, sometimes pinpointing their location to a few metres. Worried parents will be able to check up on where their children have got to after school, friends can meet for a quick drink if they see they are nearby and spouses will be able to see if their partners really are working late at the office.

Google said that Latitude was an opt-in feature, meaning that both parties have to consent to being spied on. But privacy campaigners said they were appalled by the idea, and children’s groups said the Government should intervene and look into whether the system was fully secure.

The feature was made available immediately on millions of mobile phones that can access the web, such as the BlackBerry. Within weeks Google hopes to release a version that will also work on computers as well.

“Once you’ve shared your location, you can hide it from individual friends or all of your friends at once, or you can turn off Google Latitude completely at any time.” said a Google spokesman. “You can adjust your privacy settings in Latitude so that you share as much or as little about your location as you want, with whom you want.”

Google said that it had tested the product with thousands of people to make sure that the system was secure, but experts were not so sure. Simon Davies, director of Privacy International, said the security was appalling and said Latitude would open up a “privacy minefield”. “Google is naive if it thinks there are adequate controls on this feature,” he said.

Others were concerned that even though you could, in theory, bar anyone from spying on your location, in practice peer pressure would mean it would be difficult to reject their suggestion to follow you, even if it was not in your own interests.

“It’s about the little white lies. You might be skiving off work, and now your boss might be able to see that you’re at Twickenham instead of at home,” said Ian Angell, an information expert at the London School of Economics. “You’ve already got mobile phone technology where husbands and wives track each other in secret. Google is so pervasive that this will become the rule rather than the exception.”

Google said that people always had the option of adjusting how much about their location they wanted to give away. Colleagues could merely know what city you were in, whereas other more trustworthy friends could find out what street you were walking down. How much each individual wanted to reveal was always up to them.

The technology is likely to be greeted enthusiastically by a younger generation hooked on social networking websites such as Facebook. In testing, the feature was quickly adopted by people to locate friends in crowded areas, and by families to give themselves a rough idea of when loved ones would be returning home.

Children’s groups said that, though the principle of being able to check up on the whereabouts of a child may bring peace of mind to many parents, problems would arise when children became teenagers and sought more responsibility and independence. “Is a mobile phone becoming an electronic leash on children?” said John Carr, the secretary of the Children’s Charities Coalition on Internet Safety. “You can see situations where this kind of thing might be useful, but it is also kind of imprisoning children even more.”

Mr Carr called for the Government to look into the security of the system, and said that any company that wished to offer or sell tracking software such as this should be required to get a licence.

The Information Commissioner’s office said the opt-in nature of Latitude indicated that the feature satisfied data protection laws, but said it would monitor the system closely.

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