The government is proposing to make it easier for the police to seize confidential material from journalists, it emerged on Wednesday night. Legal experts warned that the plans risked trampling on long-standing protections from the state.

The Home Office said it accepted recommendations from Lord Justice Leveson's inquiry into the media for consultation over changes to laws governing police demands for material from news organisations and reporters.

During the inquiry, the Metropolitan police urged Leveson to weaken protection for journalists from police searches and demands to hand over confidential material gained through their work.

Under the new proposals, now open to consultation, a judge would still need to approve such police requests, but the detectives would no longer have to first show they had tried to get the material from other sources.

The plans would also weaken protection for confidential material from whistleblowers. Journalists would have to show the material did not come from people who had breached confidentiality agreements or who may have committed crimes in revealing the information to a reporter. Such material if handed over could reveal the identity of sources.

Currently, the protections for journalistic materials are contained in the 1984 Police and Criminal Evidence Act (Pace).

Anti-censorship campaigners warned that the proposed changes could damage investigative journalism and the public's right to know. A leading barrister warned of a potential breach of European human rights law.

Gavin Millar QC, an expert in media law, said: "These amendments would make it much easier for the police to get orders requiring production of journalistic material. The police would not even have to try to get the evidence in other ways.

"Journalists will only be able to claim confidentiality by testifying that the source was free to give them the material. This will be impossible for most public interest disclosures by whistleblowers."

The logic for any changes is alleged abuses by News International as they tried to hamper the first Met police investigation into phone hacking in 2006.

Police believe the Murdoch-owned media company pretended to be assisting their inquiry knowing the "veneer of co-operation" would mean a judge would not grant police orders requiring the News of the World to hand over material.

The police also feel that provisions in Pace protecting journalistic material from seizure was abused by News International to stop material relating to the illegal hacking of phones being handed to detectives.

Leveson called for the review of journalist protection despite media submissions claiming that they were a "Trojan horse" that could remove protection from material such as stolen CDs used by the Daily Telegraph for its reporting on MPs' expenses.

In his report Leveson wrote: "One of the results of the legislation is that, in protecting what it is entirely appropriate to protect, there is a risk that behaviour which deserves no protection will not be uncovered.

"It makes it that much more difficult to obtain evidence to support (or, indeed, to undermine) a complaint, making much more remote the prospect of prosecution even where the true facts, if they were known, would demonstrate that such a prosecution was entirely merited."

Leveson warned that journalists should respect the protection, and not abuse it by "invoking it to cover up that which cannot be justified".

Matthew Ryder QC said: "The risk is a lower standard of protection will allow the police to obtain information from journalists that is exactly the kind of information that needs protection from the police.

"There are measures to stop the police trawling through journalists' material or documents revealing sources. Once you start unravelling that, even with the best intentions, the fundamental protections journalists need to perform the most vulnerable part of their job is lost."

Millar added: "The proposals are wholly incompatible with press freedom principles long established under European human rights law."

In a response to Leveson, to be published on Thursday, the Home Office said: "The consultation exercise will specifically consider the potential impact of the recommended change to section 11(3) of Pace on the protection of journalistic sources."

Padraig Reidy, of Index on Censorship, said: "These measures, if implemented, could have a real effect on journalism, free speech and the entire climate of freedom in the UK.

"They grievously undermine the concept of confidentiality between reporters and sources that is essential for investigative journalism."

In its response the Home Office accepted Leveson's proposal that senior police officers have to record contact with the media. Some worry this will also hamper whistleblowers.