The Serious and Organised Crime Agency is assessing the scale of corruption within the British police after concerns were raised by senior internal investigators, the Guardian can reveal.

Anti-corruption officers are worried that today's police are more vulnerable to being targeted by criminals and abusing their powers than their predecessors in the 1970s and 1980s, when corruption was thought to be at its height.

Senior figures cite three new areas where evidence suggests officers of all ranks are vulnerable to being exploited by individuals involved in crime or on the edge of criminality:

• Social networking sites, where police officers identify themselves as members of the service and are open to approaches from criminals and inappropriate associations.

• Bodybuilding gyms where officers are known to take steroids, leading them into contact with the criminal underworld and illegal drug dealing.

• The increased access by all police officers and civilian staff to confidential information in IT systems which they can leak for financial gain.

Information on the nature and scale of police corruption is shrouded in secrecy. The Soca assessment – which will be completed in April – will be a restricted document. Details of how many officers in England and Wales have been jailed for corruption and misconduct are notoriously difficult to access.

Research by the Guardian reveals that in the last 24 months at least 12 police officers have been given prison terms or have been left facing jail for corruption, and a string of internal investigations and criminal cases are waiting to be heard in the courts.

The cases include officers spending tens of thousands of pounds of public money on themselves, passing confidential information to criminals, running property scams, stealing property, brutality, having sex with women whom they have arrested, blackmailing individuals on the police intelligence database, shielding a drugs baron and tipping off an organised criminal to help him stay one step ahead of the law. The forces concerned include large metropolitan areas and rural forces and both detectives and uniformed officers were involved.

Anti-corruption investigators are becoming increasingly alive to evidence that organised criminals have planted associates with no criminal background into police forces to provide influence and information. The increasing number of organised crime gangs in Britain – more than 2,800 – and the vast amounts of money swilling around the system from the Proceeds of Crime Act, which confiscates the earnings of criminals, also increase the risk of corruption, according to experienced internal investigators.

Chief Constable Mike Cunningham, the Association of Chief Police Officers' lead on anti-corruption, said: "Over the years customs and practices in society have changed, so have the patterns of how people become corrupted.

"What hasn't changed is that some human beings are driven by personal greed or the need to appear powerful, and that poor leadership allows corruption to take place.

"Criminals want influence and information as they have always done. What we need to do is assess what the emerging threats are around corruption and retain our vigilance in the police service, because corruption is an abiding threat."

The assessment by Soca comes after the jailing this week of the Metropolitan police commander Ali Dizaei, the most senior officer for 30 years to be sent to prison for criminal abuse of his position.

Dizaei was jailed for four years for arresting and falsifying a case against a member of the public with whom he had a dispute. He was found guilty by a jury of misconduct in a public office and perverting the course of justice and accused of being a "criminal in uniform", by the head of the Independent Police Complaints Commission.

The last time such a senior officer was given a prison term for corruption was in 1977 with the jailing of Scotland Yard's Commander Ken Drury, of the Flying Squad and Wally Virgo, head of the serious crime squad – sent to prison at a time corruption was thought to be at its height. But the threat of police officers engaging in criminal misconduct remains today at every level, according to those at the cutting edge of internal investigation units, teams who are often referred to as rubber heelers, because you cannot hear them coming.

In response to the concerns, a special team within the Independent Police Complaints Commission is gathering intelligence on corruption.

Nick Hardwick, chairman of the IPCC, said the police must continue to focus on corruption despite the financial pressures they were facing. "Corruption comes in many forms and remains a threat to the police service," he said. It requires constant vigilance to fight it. Integrity must not be negotiable. I think the public will now be looking to police leadership for reassurance that they will not allow political and financial pressures to prevent them from robustly tackling corruption."

Professor Maurice Punch, a criminologist who has studied police corruption for many years, said: "The old style corruption where groups of detectives had familiar relations with criminals and met in pubs to pass on information has gone because it's too visible, it is too open to scrutiny. But new opportunities are always being created and exploited."