Britain’s surveillance laws, which have recently been used by the police to seize journalists’s phone records in the Plebgate and Huhne cases, are “not fit for purpose” and need urgent reform, a Commons inquiry has found.

The Commons home affairs select committee says that the level of secrecy surrounding use of the Regulation of Investigatory Powers Act (Ripa) allows the police to “engage in acts which would be unacceptable in a democracy”.

The committee chairman, Keith Vaz, said the surveillance law was not fit for purpose: “Using Ripa to access telephone records of journalists is wrong and this practice must cease. The inevitable consequence is that this deters whistleblowers from coming forward.”

The MPs’ inquiry followed claims by Sun and Daily Mail journalists that the Metropolitan and Kent police forces were secretly using the powers to trawl through thousands of phone numbers to detect their confidential sources in high-profile stories.

In response Home Office ministers have said they will revise the Ripa rules on communications data requests involving sensitive professions such as journalists and lawyers, and they will launch a consultation on the move before Christmas.

The inquiry found the law enforcement agencies routinely fail to record the professions of those whose communications data records they access under Ripa.

“The recording of information under Ripa is totally insufficient, and the whole process appears secretive and disorganised with information being destroyed afterwards,” concludes their report published on Saturday.

The MPs say they fully share the concern expressed by the National Union of Journalists that their sources of information should be fully protected, and acknowledge that journalists have gone to prison on occasions rather than reveal where their information came from.

The NUJ told the MPs that the Ripa allegations had sent a shockwave through the industry over their potential impact on sources and whistleblowers.

The committee said that while they understood the need for secrecy during the course of investigations and in the aftermath they were concerned that the level of secrecy surrounding the use of these powers allowed the police to engage in acts which are unacceptable in a democracy.

The MPs recommend that the Home Office ensure that the police employ Ripa powers properly and that the code on its use is updated to include special provisions for dealing with privileged information such as journalistic and legal material.

The security minister, James Brokenshire, said: “A free press is fundamental to a free society and the government is determined that nothing is done which puts that at risk. Communications data is an absolutely critical tool used by police and other agencies to investigate crime, safeguard national security and protect the public. There are measures in place to ensure that police powers to access this data are not abused.”

Brokenshire added that ministers were working to ensure that extra consideration be given to a communications data request involving those in sensitive professions, such as journalists, and a consultation would be launched before Christmas.

Major reviews of the surveillance laws are under way by the official terror laws watchdog, David Anderson QC, and the parliamentary intelligence and security committee. A specific investigation is also being conducted by the interception of communications commissioner.