The leading public sector union is advising council employees not to provide fingerprints, after Westminster City Council installed biometrics machines without consulting staff.

Unison believes the introduction of the machines, which read fingerprints of staff " clocking in and out," breaches confidentiality and data protection policies, and that the move has been triggered by suspicious management.

The council cannot be relied on to adequately manage this data, said Stephen Higgins, Westminster Unison assistant branch secretary.

"We already have serious concerns about breaches of confidentiality and data protection between the City Council and the Metropolitan Police involving our members," he said.

"We simply do not trust the City Council to hold this information securely and see no justification for such a scheme."

In a statement, Unison pointed out under the Data Protection Act, personal data shall be adequate, relevant and "not excessive in relation to the purpose or purposes for which they are processed."

Unison has issued a letter to members advising them not to provide fingerprints, and to present it to managers when asked to cooperate with the policy. If Westminster does not rethink its proposals, the union will complain to the Information Commissioner.

"The intention of the City Council to obtain the fingerprints or other biometric data from staff is a disproportionate and excessive step which is based on mistrust," said Phil Vaughan Westminster Unison Branch Secretary.

"We can see no justifiable reason why it is necessary for the City Council to obtain such personal data, and Westminster Unison shall resist such draconian measures."