Campaign group Big Brother Watch found that 904 police officers and staff were subjected to internal disciplinary procedures, and 243 received criminal convictions, for breaching the Data Protection Act. Ninety eight were fired. The group made a host of FoI requests covering the period from 2007 to 2010.

The news comes only two weeks after the launch of the Police National Database, which is intended to securely hold data on millions of victims of crime nationally, as well as suspects and convicted criminals. Campaigners have questioned the security of the data, though the National Police Improvement Authority insisted that it is the "most secure police system developed to date".The release of the figures also follows allegations that former News of the World editor and Downing Street communications boss Andy Coulson paid the police to access confidential data.

The areas where the largest number of officers and police staff were subjected to internal disciplinary procedures for DPA breaches since 2007 were: Merseyside (208), West Midlands (83), Humberside (62), South Yorkshire (42), and Northumbria (39).

"Our investigation shows that not only have police employees been found to have run background records checks on friends and possible partners, but some have been convicted for passing sensitive information to criminal gangs and drug dealers," said Daniel Hamilton, director at Big Brother Watch.

"This is at best hugely intrusive and, at worse, downright dangerous."