(CNN) -- Journalists working for a large British newspaper group have been asked to give a written promise that they have not been involved in phone hacking or other illegal activity, the company said Friday.
The request from Trinity Mirror, publisher of papers including the Daily Mirror, follows the launch last month of a judicial inquiry into press conduct in the wake of a phone-hacking scandal that engulfed a rival newspaper group, News International.
Police have also been investigating claims of phone hacking and bribery by staff at the now-defunct News of the World newspaper, run by News International as part of Rupert Murdoch's News Corp. empire.
Trinity Mirror said in a statement that it had "sought and received formal written confirmation from senior editorial executives" across its national and regional titles that since new laws came into force in 2000 "and whilst an employee of the Group they have not nor, to their knowledge, have any of their staff or anyone on their behalf, intercepted any telephone messages, made payments to serving police officers or accessed the police national computer."
Trinity Mirror said it had also "implemented a review of its editorial controls and procedures" following the announcement of the judicial inquiry, led by Lord Justice Leveson, and the introduction of new internal systems.
"It is too early to determine what, if any, impact there will be on our businesses from either review," the company said.
Asked whether written promises could extend to former staff, Rich Ellis, head of communications at Trinity Mirror, said, "We are only in a position to ask current employees to write these guarantees."
Trinity Mirror would make no further comment.
A dozen people have been arrested in connection with allegations that journalists from News of the World hacked into voice mails of people ranging from celebrities to crime victims and illegally paid police for information.
The latest to be arrested, a 61-year-old man, was released on bail Thursday, police in London said, a day after he was detained on suspicion of unlawful interception of communications and conspiring to intercept communications.
The scandal around News of the World has raised questions about whether other news organizations also engaged in misconduct.
News of the World was shut down last month after outrage over claims that the voicemail of murdered British teenager Milly Dowler was among those hacked by its staff, potentially hindering a police investigation.
A police review board said this week that London's top police spokesman is now under investigation for possible "gross misconduct" in connection with the phone-hacking scandal.
Dick Fedorcio, the head of public affairs for the Metropolitan Police Service, has been placed on "extended leave" while the investigation is under way but will be allowed to work from home, the Independent Police Complaints Commission said in a statement.
Fedorcio has come under scrutiny in the investigation through his ties to Neil Wallis, a former News of the World executive editor the Met hired as a public relations consultant.
CNN's Anna Stewart contributed to this report.