 
           Google admitted in May 2010 its Street  View cars had mistakenly collected private information as they  photographed homes and landmarks.  Photograph: Sean Gallup/Getty Images
Google is facing a fresh privacy blunder after it admitted it  had not deleted all of the private data, including emails and passwords,  it secretly collected from 
internet users around the UK.
The search giant was ordered in December 2010 to delete the private information hoovered up by its Street View cars from open 
Wi-Fi networks.
But on Friday 
Google told the Information Commissioner's Office that human error prevented it from erasing the data, which could include the emails and passwords of millions of Britons.
Google  admitted in May 2010 its Street View cars had mistakenly collected  private information as they photographed homes and landmarks around the  world.
It is not known exactly what private information was taken  in the UK, but regulators in the US found traces of medical records and  web browsing history among the so-called "payload" data.
The news  that Google has not purged all of the data taken from UK users 19 months  after it was instructed to do so will cause further embarrassment for  the company.
On Friday, the ICO said the retention of the data appeared to be a breach of the undertaking signed by Google in December 2010.
A  spokesman for the ICO said it would now conduct a forensic analysis of  the data, meaning Google could be fined up to £500,000 if the material  is found to be in breach of the Data Protection Act.
The company will be one of the first to have breached an undertaking by the ICO if the data is found to be in breach of the DPA.
The  ICO said in a statement: "The ICO is clear that this information should  never have been collected in the first place and the company's failure  to secure its deletion as promised is cause for concern."
Google's  global privacy counsel, Peter Fleischer, apologised for the error in a  letter to the ICO on Friday. Google declined to comment beyond the  letter, which was 
published on the ICO website.
The technology company is already being investigated by the ICO over claims it orchestrated a 
cover-up of the data collection in 2010.
Google declined to say when it realised it had not deleted all of the data.
Nick  Pickles, director of privacy at the pressure group Big Brother Watch,  said Google should never have been ordered to erase the information in  the first place.
"We now have an opportunity to explore just how sensitive the information was," he said.
"Given  that Google failed to respect people's privacy in the first place and  subsequently failed to adhere to its agreement with the information  commissioner, serious questions need to be asked to understand why  Google seemingly sees itself as above the law.
"The information  commissioner is hampered by a woeful lack of powers and is forced to  trust organisations to tell the truth. Given Google's behaviour has  called into question if that really is a proper way to protect our  personal data, it must be right to now demand a proper regulator with  the powers and punishments to fully protect British people's privacy."