There are many reasons why Rupert Murdoch will be alarmed at this latest development in the long-running phone hacking scandal at the fenced compound in Wapping, east London, that houses the media mogul's stable of British newspapers, News International.

Foremost among his concerns will be the threat of damage to The Sun, the paper which he bought for £800,000 in 1969 and a title that is especially close to his heart and highly profitable. The paper has managed to remain distant from the stain of phone hacking that has besmirched its sister publication, the News of the World, causing criminal proceedings, civil actions and parliamentary hearings.

The Sun is a lucrative operation and recently reported a record year for advertising. News Group – the section of News International that includes The Sun and the News of the World – is making an annual profit of £40m, while Times Newspapers (The Times and The Sunday Times) is losing £45m a year.

Furthermore, Mr Murdoch, who flew to London to try to limit the damage being caused by the affair to his ongoing and critical bid to take outright control of BSkyB, will be concerned that Andy Gilchrist's allegations may create further difficulties for Rebekah Brooks, who was editing The Sun at the time stories were published about the Fire Brigades Union leader.

As chief executive of News International, Ms Brooks is already overseeing an internal review of the extent of phone hacking at the News of the World under the editorship of her friend Andy Coulson. The inquiry has caused the sacking of the paper's assistant editor (news), Ian Edmondson. The royal editor, Clive Goodman, was jailed in 2007.

When editing The Sun, Ms Brooks was embroiled in controversy when she admitted to MPs that the newspaper paid police officers for information. But the daily title has been untainted by phone hacking. Indeed, the current Sun editor, Dominic Mohan, publicly complained as far back as 2002, when he was a show business journalist, how media rivals were obtaining scoops by exploiting failings in telephone security. Mohan will be unhappy that his paper must now answer allegations that it adopted similar tactics.