POLICE are building an “impenetrable wall of silence” around their darkest secrets and practices, according to a report published today.

Sir John Mitting, the new chair of the public inquiry into undercover policing, will make a statement next month on the “future conduct” of the troubled probe at a preliminary hearing.

The inquiry was set up by the government following revelations that officers infiltrated activist groups and trade unions, deceiving women activists into long-term relationships.

But two years after its launch, the inquiry has still not heard any evidence — and victims of undercover spying have accused the Metropolitan Police of obstructing its progress.

Now a new report from the Centre for Crime and Justice Studies says there is “no clear avenue for establishing the most basic of facts” for “deceived, stonewalled” activists.

The report, titled The Undercover Policing of Political Protest, says the current set-up for disclosure of information leaves an “immense concentration of power in the hands of the police.”

Since the inquiry was established, the Met has strongly resisted the publication of officers’ cover names and has been accused of destroying files relating to undercover activities.

Yesterday Mr Mitting announced he was “minded to” publish the cover names of four further undercover officers and the real name of one.

The report’s author Helen Mills, a senior associate of the centre, said: “The slow progress of the undercover policing inquiry means that many victims of police spying, as well as wider public, are questioning whether the police will ever be held to account by the people they purportedly serve.”

Officers of elite police squads infiltrated campaign groups on a long-term basis. Some information gathered on union activists was supplied to a secretive cartel of construction companies for a blacklist of safety representatives and so-called troublemakers.

Police also spied on anti-racist campaigners and the family of murdered teenager Stephen Lawrence.

Stafford Scott, who was spied on as an activist in the Broadwater Farm Defence Campaign, said: “If the police have their way, this will be the most secretive public inquiry to have ever taken place.

“It will be a public inquiry where even the victims of the spycops will not be allowed to see the faces, or learn of the identities, of the police officers.

“We need a very public inquiry, where no officer of the state is allowed to hide behind their office. A public inquiry where the search for truth far outweighs the needless secrecy and cover-up that we are currently witnessing.”