The number of surveillance requests made by public officials for telephone and internet details exceeded 500,000 last year, according to new figures.

The 520,000 requests, equivalent to around 1,400 per day, represent a huge increase on 2006 and 2005 which recorded an average of fewer than 350,000.

Requests from police, security services and other public bodies for billing details and other information are legitimate under the Regulation of Investigatory Powers Act.

Existing powers allow public officials to see details such as website records and itemised phone bills, although the monitoring of conversations is not permitted.

Local authorities were singled out for their perceived misuse of existing legislation, even though they accounted for a small number of the overall requests.

Interception of Communications Commissioner Sir Paul Kennedy said in his report that local authorities "could make much more use of communications data as a powerful tool to investigate crime".

In a separate report Chief Surveillance Commissioner Sir Christopher Rose called for improvements in the way local councils use the powers.

Sir Christopher said that some local authorities had a "tendency to expose a lack of understanding of the legislation" and demonstrated a "serious misunderstanding of the concept of proportionality".