Police officers should be prevented from accessing people's personal mobile phone data without a search warrant, a privacy campaign group has said.

At least 26 police forces in England and Wales have begun using new technology to extract data from phones.

And Privacy International said there had been no public debate about the rapid rollout of this practice.

But one former chief constable said obtaining a warrant in each instance would be "just not practical".

Privacy International obtained the figures through Freedom of Information requests to 47 forces, of which 42 responded.

It told the BBC's Victoria Derbyshire programme that most people were unaware of their rights.

And it is calling for an immediate review of current practice and a public-awareness campaign.

The technology allows officers to extract location data, conversations on encrypted apps, call logs, emails, text messages, passwords, internet searches and more.

It can be used on suspects, victims and witnesses.

It also downloads deleted data, including messages sent to the phone by other people.

It has been trialled in Scotland. It is not being used in Northern Ireland.

'Investigative requirements'

The extraction devices used generally take everything of one type off a phone - so if a witness's mobile contains a photo important to an investigation, the device will download all photos.

The National Police Chiefs Council said the decision to download phone data was a judgement that could be made on a case-by-case basis "defined by the investigative requirements of the case".

But Privacy International said it feared there was no national oversight, and no clear guidance on when to delete the data.