One privacy campaigner described the intrusion as "absolutely scandalous" and called on Google to launch a full inquiry into the affair.

The Information Commissioner's Office (ICO), the privacy watchdog, said it would be looking into Google's admission.

Images for Street View were gathered by vehicle-mounted panoramic cameras starting in 2008.

In May this year, Google confessed the vehicles had also been gathering information about the location of wireless networks, the devices which connect computers to the telecommunications network via radio waves.

Now the California-based company has revealed that far more information was harvested than was previously thought, after privacy regulators in seven countries analysed the data.

"It's clear from those inspections that while most of the data is fragmentary, in some instances entire emails and URLs [web addresses] were captured, as well as passwords," said Alan Eustace, Google's vice-president of engineering and research.

"We want to delete this data as soon as possible, and I would like to apologise again for the fact that we collected it in the first place."

Street View pictures were taken in the UK, US, Germany and other countries. Sources told The Sunday Telegraph that Britain was among countries affected by the privacy breach.

The company archived all the material it had gathered, which included emails being sent by private individuals, the web pages they were viewing and passwords they may have entered as the Street View vehicle passed their homes.

It is believed that only wireless networks that were not password-protected were affected.

Simon Davies, director of Privacy International, said: "It's absolutely scandalous that this situation has developed and so many people have had their communications intercepted.

"The company must launch a full inquiry and produce a public report on exactly what happened, as well as release the audit it has already undertaken.

"There are a lot of questions that need to be answered about how and why the company did this."

Privacy International lodged a complaint with Scotland Yard earlier this year about Google's Street View activities and officers are still considering whether a crime has been committed.

Google is facing prosecution in France and a class action in the US, with similar lawsuits pending in other countries.

Street View, which allows internet users to examine photos of street scenes and view close-up images of almost every property, attracted controversy from the moment it was launched in Britain in March last year.

Critics said the photographs themselves invaded privacy and provided burglars with an invaluable research tool.

Individuals who could been seen in the photos included a man emerging from a sex shop in London's Soho; children throwing stones at a house in Musselburgh, Scotland; a man vomiting outside a pool hall in east London; and three police officers arresting a man in Camden, north London.

A Google spokesman said the wireless data was gathered so the company could amass details of "Wi-Fi" hot spots that could help provide location-based web services.

Collection of the additional data was a mistake resulting from a piece of computer code from an experimental project being accidentally included in the Street View cars' software, it added.

The ICO spokesman said: "We understand that Google has accepted that in some instances entire URLs and emails have been captured.

"We will be making inquiries to see whether this information relates to the data inadvertently captured in the UK before deciding on the necessary course of action, including a consideration of the need to use our enforcement powers."

Daniel Hamilton, campaign director at privacy group Big Brother Watch, said: "The harvesting of sensitive personal information like this is completely unacceptable. Google is fast developing a reputation as a company that cares little for privacy or data security."

In March this year Google announced that 95 per cent of Britain's roads had been covered by Street View, amounting to nearly a quarter of a million miles from Penzance to the Shetland Isles.

The camera vehicles are still at work on Britain's roads, collecting new images and filling in gaps which remain in the panoramic sequences.