The RSPCA is using a sensitive police database nearly 1,500 times a year under a deal giving it privileged access to criminal records.
The animal welfare charity is using the Police National Computer (PNC) an average of 124 times every month in relation to prosecutions it brings.
The scale of its activity raised concerns yesterday as the records are usually regarded as so sensitive that employers – even in the public sector and involved in working with children – do not have access to them.
Critics accuse the charity of increasing ‘militancy’ by focusing on expensive political stunts and strong-arm tactics at the expense of its core mission to protect animals.
Information Commissioner Christopher Graham is to investigate the deal struck in 2010 between the police and the RSPCA.
Under the agreement with the Association of Chief Police Officers (Acpo), a private company, the RSPCA can request a criminal record check, paying Acpo at least £35 per search.
Last night Tory MP Simon Hart, former head of the Countryside Alliance, said: ‘If any other political organisation had access to the PNC there would be widespread public concern.
‘This is an increasingly politically driven animal rights group which is a shadow of its welfare origins. I will be writing to the Home Secretary and Attorney General to seek clarity as to whether any pressure group can have similar access.’
The deal allows the RSPCA to request information about the criminal records of suspects, witnesses, defendants and victims.
But the bulk of its use of the PNC came as RSPCA officials created fresh records on the database of their own suspects.
During the same 19-month period the charity added 2,311 records of people it intended to prosecute so that their data could be seen by police.
Other organisations holding agreements with Acpo are state bodies such as the Civil Aviation Authority and the Food Standards Agency.
The RSPCA, which yesterday revealed that it secured 4,168 animal welfare and cruelty convictions last year, up from 2,441 three years ago, claims it accesses the computer to update records of its prosecutions.
But it has been severely criticised in recent months for being too aggressive in prosecutions and campaigns.
A Conservative councillor who served as election agent for James Gray, a pro-hunting MP, was prosecuted for unlawful hunting, but the case was dropped at the 11th hour. A judge criticised the animal charity for bringing the prosecution even though nobody had seen a fox.
Sir Barney White-Spunner, who heads the Countryside Alliance, called for the RSPCA’s access to police files to be stopped until it is proved lawful.
He said: ‘The RSPCA is neither a public body nor a statutory prosecuting force, it is a campaigning charity with an increasingly militant animal rights agenda.
‘The disclosure of highly personal information held on police databases to the organisation could pose significant risks to the individual concerned.’
An Acpo spokesman said the charity has ‘indirect’ access, which does not include firearms licensing, vehicle registrations or information unrelated to particular prosecutions.