A local authority has lost an unencrypted memory stick with details of children's and young people's mental and physical health as well as their ethnicity, privacy watchdog the Information Commissioner's Office (ICO) has said.

The details, said to be of 'a handful' of children, would be available to anyone finding the memory stick, which was unencrypted and not password protected.

West Berkshire Council has promised the ICO that it will improve the way that it handles personal data. It has signed a formal undertaking that commits it to encrypting all mobile and portable devices and training staff in data protection policies.

The incident is the second to be reported in six months involving the Council. An ICO spokesman said that the previous incident had been resolved "informally".

Investigating the loss of the memory stick, the ICO said that it had discovered that the Council's data protection processes were inadequate.

"The ICO found that unencrypted devices, in operation before the council introduced encrypted memory sticks in 2006, were still being used by members of staff. Further enquiries revealed staff had not received appropriate training in data protection issues and monitoring of compliance with the council’s policies was found to be inadequate," the ICO said.

The memory stick which was lost was used in schools and dated from 2005, the spokesman said. He said that the employee who lost it was not sure how many children's details were on it.

"The amount of data on it varied from day to day, though we know it was more than one or two; the employee was working at a local school that day," said the spokesman, who said that it contained the details of "a handful" of people.

West Berkshire Council chief executive Nick Carter has signed a formal Undertaking with the ICO pledging more training for staff on the Council's data protection policies, the ICO said.

“It is essential that organisations ensure the correct safeguards are in place when storing and transferring personal information, especially when it concerns sensitive information relating to children," said ICO enforcement group manager Sally-Anne Poole.

"A lack of awareness and training in data protection requirements can lead to personal information falling into the wrong hands. I am aware that [West Berkshire] staff have been provided with encrypted USB sticks since 2006 but older devices were not recalled," she said. "I am pleased that the council has now taken action to prevent against further data breaches.”