News UK is facing new claims that The Sun was involved in phone-hacking.
The company has said the claims are "unsubstantiated" and that if they proceed it will "defend them vigorously".
Today, a case management was held in the third tranche of phone-hacking claims against the News of the World.
The claims all involve people who claim their voicemails were intercepted by Dan Evans when he moved from the Sunday Mirror to the News of the World.
The High Court in London today heard that the claimants want to argue that hacking happened outside the agreed timescale of 1 January 2005 to 8 August 2006, that journalists other than Evans were involved and that the hacking also extended to The Sun.
If phone-hacking was found to involve The Sun this would escalate litigation for News Group Newspapers (NGN, part of News UK) – just at the point when it appeared to be ending.
The 16 claims are due to go to trial in April. The court heard that there are another 25 claimants in addition to this 16.
The court heard that five new defence witnesses have come forward with phone-hacking allegations dating back to 1998 and that a number of these were former NGN journalists.
Lawyer for NGN Anthony White QC told the court: “If we have to put in place a disclosure regime going back to 1998 [at The Sun] we will have to do so from scratch.”
He said involving The Sun in phone-hacking civil claims would be a “big development” and “open up a new front in this litigation”.
He said that disclosures of information relating to the News of the World and phone-hacking going back to 2000 had cost £13m.
The court heard that the various phone-hacking claims against the News of the World were now entering their “twilight” stage, with no new claims issued against the paper since March.
Lawyers for NGN indicated that they would need a period of some weeks to assess the new evidence before making presentations on the application to involve The Sun in phone-hacking litigation.
The judge said that he would give his decision on whether to allow the claims to be brought against The Sun before Easter.
Among the 16 claimants in the latest round of the litigation are Simon Clegg, the former chief executive of the British Olympic Association.
EastEnders actors Christopher Parker and Brooke Kinsella and Coronation Street actors Kym Marsh, Samia Ghadie and Alan Halsall also feature in the list.
Others are designer Pearl Lowe and her musician husband Danny Goffey and Leslie Heseltine who is better known as actor and comedian Les Dennis.
A spokesperson for News UK said: "Following many years of investigation, there were no charges against The Sun or its employees for voicemail interception. Today, certain claimants seeking financial settlements arising from activities at the News of the World have made unsubstantiated claims against The Sun. If the court permits such claims to proceed, The Sun will defend them vigorously.”
Research by the Media Standards Trust published in March 2015 found that 591 people had settled phone-hacking claims with News UK over the activities at the News of the World.
News UK, formerly News International, has been dealing with civil legal claims related to phone-hacking since 2008 at a total cost well in excess of £300m.
Trinity Mirror is facing at least 158 civil claims for damages over phone-hacking at the Daily Mirror, Sunday Mirror and Sunday People.