Harbottle & Lewis has issued a letter in response to allegations in the press that the firm made a mistake in its part in an internal investigation into phone-hacking at News International.

In an open letter sent earlier today (18 July), Harbottle said that its ability to respond to the allegations made last week by News Corporation head Rupert Murdoch were constrained by factors including client confidentiality.

Harbottle's letter states: "Despite the constraints upon us, we can make it clear that many recent press reports have not accurately described the extent of our retainer from News International in 2007. Unfortunately we are not at present able to correct these errors by explaining what the scope of that retainer was, since that is (or at least may be, depending on technical legal arguments) privileged information.

"All of these issues will no doubt become clearer in due course, especially when all of the relevant parties co-operate fully with the various investigations and inquiries. In the mean time, we will say more as and when it becomes professionally possible to do so."

The law firm has also appointed PR consultancy Luther Pendragon to represent it in the matter.

In a separate development, News Corp has appointed Lord Grabiner QC (pictured) to chair a high-level standards committee charged with leading the company's response to the wider hacking claims.

The One Essex Court heavyweight – one of the top commercial silks in the UK – will chair the committee, which News Corp said in a statement is "authorised to co-operate fully with all relevant investigations and inquiries in the News of the World phone hacking case, police payments and all other related issues across News International, as well as conducting its own enquiries where appropriate."

Harbottle's statement comes after Murdoch alleged in an interview with The Wall Street Journal published last Friday (15 July) that Harbottle made "a major mistake" in its role reviewing a number of emails from staff at now-defunct Sunday tabloid the News of the World (NoW).

The investigation saw Harbottle's former managing partner, Lawrence Abramson, confirm to News International director of legal affairs, Jon Chapman, in 2007 that it had not found anything in the emails to suggest that phone hacking went further than former NoW royal editor Clive Goodman, who was jailed in 2007, or was known about by management such as Andy Coulson.

News International subsequently concluded as a result of its internal investigation that Goodman acted alone. Harbottle's advice was disclosed to a Parliamentary committee in 2009.

A spokesperson for Lawrence Abramson, who left Harbottle last year to join Fladgate, issued the following statement on his behalf: "My previous statement – 'Professional duty of confidentiality prevents me from commenting on this' – remains the case. I am not in a position to comment any further."

Since Murdoch openly criticised Harbottle, the firm has come in for additional criticism in the press, with reports this weekend suggesting that Labour MP Tom Watson has called on the Solicitors Regulation Authority to investigate Harbottle.

An SRA spokesperson said the body was unable to comment on individual investigations but added in a subsequent statement: "As with any high-profile case, we are monitoring the situation closely to determine what, if any, regulatory approaches we need to take. We do not generally disclose details of our inquiries at early stages, to avoid prejudicing any regulatory action."

However, Watson confirmed to Legal Week via Twitter that he had made the referral to the SRA.

Separately, Watson has also called on the Serious Fraud Office to investigate alleged payments made by News International to victims of the NoW's phone-hacking.

The SFO said in a statement: "The SFO can confirm that it has today received a letter from Tom Watson MP calling upon the SFO to investigate certain allegations relating to News Corp. SFO director Richard Alderman will give full consideration to Mr Watson's letter. The SFO is aware that the Metropolitan Police Service is conducting an investigation into alleged improper payments to police officers."

The SFO also confirmed that it had been talking with US authorities and was ready to assist them if they chose to open an investigation into News Corp in the US.

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