The publisher of the Daily Mirror has admitted its senior editors and executives “actively turned a blind eye” to phone hacking for years as it agreed to pay hefty damages to Hugh Grant to settle his high court claim on Monday.

Mirror Group Newspapers (MGN) acknowledged that people working at its newspapers were involved in a widespread campaign of “unlawful information-gathering”; a campaign they then tried to cover up.

The firm accepted that “senior employees, including executives, editors and journalists, condoned, encouraged or actively turned a blind eye to the widespread culture of unlawful information-gathering activities at all three of its newspapers for many years and actively sought to conceal its wrongdoing from its many victims of intrusion”, Grant’s solicitor, Anjlee Saigol, told Mr Justice Mann at the high court .

Reading a statement agreed by Grant and the publisher, Saigol added that MGN had acknowledged its “repeated and prolonged intrusions into innocent people’s lives over, in some instances, a decade, could have been prevented or interrupted”.

Instead, the statement said, the parent company Trinity Mirror “failed to properly investigate these disgraceful actions” when allegations first emerged in 2006.

The admission goes yet further than the fulsome concessions made by MGN when it settled a similar case brought by the actor and comedian, Steve Coogan, last October. At that point, the firm acknowledged Coogan had been the “target of unlawful activities and that these activities were concealed until years later”.

For his part, Coogan said editors and executives, among them Piers Morgan, had not yet been “subjected to proper scrutiny” and called for the second part of the Leveson inquiry into the British press to take place.

Speaking outside of court on Monday, Grant echoed that call, saying: “This case was not just about what they did to my phone and those close to me … This litigation has made clear that phone hacking and other unlawful information-gathering took place on an industrial scale at the Daily Mirror, Sunday Mirror and Sunday People.“This newspaper group has misled the public and its shareholders for many years, and it has let down its readers and its hard-working journalists. The public were not told the truth, the victims were not told the truth, the shareholders were not told the truth and the Leveson inquiry was not told the truth. That is why the second part of the Leveson inquiry must take place – to get to the truth and discover who broke the law and who lied about it.”

Saigol, of Taylor Hampton solicitors, told the judge: “Mr Grant brought this action in relation to alleged illegal misuses of his private information, obtained by hacking into his voicemails, as well as blagging and surveillance, committed by MGN’s journalists at all three of its newspapers over, as MGN now accepts, many years.

“Although Mr Grant now has some clarity as to the extent of MGN’s unlawful activities in relation to him, one of his principal reasons for pursuing this case was to uncover and establish the wider truth about MGN’s investigations into and knowledge of its unlawful activities before it finally admitted these practices in September 2014.”

Alex Wilson, for Mirror Group Newspapers, said: “MGN accepts that the unlawful interception of voicemail messages and procurement of private information about the claimant and others should never have happened. MGN acknowledges that was morally wrong and deeply regrets the wrongful acts of its former employees which caused damage and distress to those affected.”

Saigol told the court Grant had been “frustrated certain editors and executives gave evidence denying knowledge of phone hacking at MGN’s titles and suggesting that they had seen no evidence to show it had taken place”. She said he had “found the evidence given to the [Leveson] inquiry on behalf of Trinity Mirror difficult to believe”.

The publisher paid “substantial damages”, believed to be a six-figure sum. Saigol said her client donated the money to Hacked Off, the campaign group that has fought tabloid newspapers over their use of phone hacking.

The judge also heard details of settlements against Mirror Group Newspapers by the actor Ralf Little and Rupert Lowe, who was the executive chairman and joint managing director of Southampton football club between 1999 and 2006. Both men received undisclosed damages payouts and apologies from MGN.