Whistleblowers need better legal protection because they are far easier to identify in the digital era and successive laws have undermined their status, according to a report by media lawyers.

The study by the Institute of Advanced Legal Studies (IALS) at London University says journalists find it increasingly difficult to safeguard the anonymity of their sources due to the monitoring and interception of online and phone conversations. The study, which will be launched in the House of Lords on Wednesday, is supported by the Guardian.

The warning follows the publication earlier this month of a Law Commission review on how to update the Official Secrets Act. It suggested that prison sentences for leaking official information could be significantly increased and dismissed the idea of introducing a public interest defence. The commission’s proposals were widely condemned by whistleblowers and human rights organisations.

The report, Protecting Sources and Whistleblowers in a Digital Age, identifies weaknesses introduced by the Investigatory Powers Act (IPA) and, potentially, the digital economy bill that is going through parliament. The IPA declares that communications metadata – which could be used to hunt down and prosecute a source – belongs to the telecoms provider not the journalist.

“Legal protections [for whistleblowers],” the report says, “have become ineffective ... If covert powers are used, a journalist and a source will not know this has occurred – intrusion may become apparent only if the material is used in legal proceedings.”

The study notes that Lord Justice Leveson, in his inquiry into the practice and ethics of the press, also recommended narrowing the protection afforded to journalists when seeking orders for disclosure of material under the 1984 Police and Criminal Evidence Act.

Protecting confidential sources is a principle supported by the National Union of Journalists (NUJ) in its code of conduct. In the past, reporters have risked jail rather than reveal who gave them information for stories on matters of public interest.

Following lobbying by the NUJ, the recently reformed clause 37 of the digital economy bill does create a defence for publication in the public interest. The IALS report, however, warns that uncertainties remain about how the defence will be interpreted by the courts.

It notes: “It is a thorny legal problem about what should be considered as ‘journalism’, and so it is difficult to predict who – or what activity – will benefit from this defence. Additionally, even if journalists are better protected in law, we must not neglect the question of whether sources and whistleblowers are adequately protected.”

The report calls for the IPA to be rendered compliant with the UK’s international human rights obligations so journalists and their anonymous sources are sufficiently protected.

In a foreword to the report, the editor-in-chief of the Guardian, Katharine Viner, says: “At a time when journalistic protections are more important than ever, the UK parliament has just passed [the Investigatory Powers Act] that brings in one of the most draconian surveillance regimes anywhere in the world. It enables law enforcement and agencies to access journalists’ data without the journalists ever knowing.”

Commenting on the Law Commission proposals, Judith Townend and Richard Danbury of the IALS said: “A consolidating act that replicates the deficiencies of already existing [Official Secrets Act] law is no improvement on the existing law, and the absence of a public interest defence in actions that relate to whistleblowing of officially secret material is – in our view – a significant omission.”

Gill Phillips, the Guardian’s editorial legal director, who contributed to the report, said: “Existing legal source protection framework [for whistleblowers] in the UK is being eroded by national security and anti-terrorism legislation, undercut by surveillance and jeopardised by the imposition of data retention obligations on third-party intermediaries such as internet service providers and telecommunications companies.”

A government spokesperson said: “Far from weakening protections for sources as this report suggests, this government has strengthened safeguards through the Investigatory Powers Act. Now any public body seeking to use communications data to identify a journalist’s source must first gain approval from a senior judge.

“We believe in the freedom of the press, and would never do anything to undermine legitimate whistleblowing or investigative journalism – it’s not government policy and never will be.”