Google has agreed to delete private emails and passwords mistakenly picked up from wireless networks in Britain by its Street View cars, the British information commissioner said today.

The US Internet giant has also agreed to improve the way it trains staff on data protection issues as it seeks to manage a global row over the cars, which gather information for its free online mapping services.

"I welcome the fact that the Wi-Fi payload data that should never have been collected in the first place can, at last, be deleted," said Information Commissioner Christopher Graham, Britain's data protection watchdog.

He added: "I am very pleased to have a firm commitment from Google to work with my office to improve its handling of personal information.

"We don't want another breach like the collection of payload data by Google Street View vehicles to occur again."

Graham said this month that Google had committed a "significant breach" of British law when its Street View cars picked up private data but said it would not be fined as long as it promised not to do so again.

In the agreement announced today, which was signed by Google senior vice president Alan Eustace, the firm said its purpose had been to identify Wi-Fi networks and to map where they were for location-based mobile applications.

It has now agreed to "delete payload data that has been identified as having been collected by Google in the UK, to the extent that Google has no other outstanding legal obligation to retain such data".

A Google spokeswoman said: "We're pleased that the ICO (Information Commissioner's Office) have concluded their investigation and we will be working to delete the data as soon as possible."

The firm will also boost training for engineers and other staff about the collection and use of private data and allow Graham's office to conduct an audit of its privacy training programmes and privacy reviews of new products.

Google announced in May that its Street View cars, taking photographs of cities in more than 30 countries, had inadvertently gathered data sent over unsecured Wi-Fi systems, sparking complaints by data regulators worldwide.

It has since stopped the collection of Wi-Fi data by Street View cars.