Two companies have been found in breach of the Data Protection Act after tens of thousands of tenants' details were left at a London pub, alongside 800 records with bank account details.

A contractor managed to lose data on tenants of two separate housing companies Wandle Housing Association and Lewisham Homes.

The contractor was working for the latter organisation when he lost an unencrypted USB, which contained data copied from both companies' networks.

Saving personal information on to an unencrypted memory stick is as risky as taking hard copy papers out of the office.

The device contained details of over 20,000 tenants of Lewisham Homes and 6,200 from Wandle Housing Association. Almost 800 of the records belonging to Lewisham Homes also contained tenants' bank account details.

The USB stick was recovered and handed into police.

"Saving personal information on to an unencrypted memory stick is as risky as taking hard copy papers out of the office," said Sally-Anne Poole, acting head of enforcement at the Information Commissioner's Office (ICO).

"This incident could so easily have been avoided if the information had been properly protected."

The two housing companies have agreed to ensure all portable devices are encrypted. Contractors, as well as other staff, will also have their personal data handling monitored.