Rupert Murdoch's News International, which owns The Times and The Sun newspapers, has appointed law firm Linklaters to trawl through thousands of emails under a fresh internal investigation into phone hacking.

The email search is expected to form a major part of the internal review, which will also see journalists interviewed and financial records examined. Both parties declined to comment on which emails will be examined, but it is thought that the publisher is preparing for an extensive search through its archive.

It remains unclear which emails will be made available to Linklaters. A previous internal investigation at News International in 2007 reportedly only looked at around 2,500 emails, with around 300 handed to law firm Harbottle & Lewis, the firm tasked at that time with reaching a conclusion on the company's practices. The number was described as low considering reporters often deal with hundreds of emails every day.

It has also been reported that News International had ordered the deletion of many emails. Lawyers observing the case have said that while this was entirely legal, any message deletion would be viewed unfavourably when a criminal investigation is pending.

The police are understood to be trawling through thousands of News International emails, beyond just those examined by the company in its previous investigation.

Questions remain as to whether Rupert Murdoch's son James, chairman of News International, saw an email that suggested phone hacking was more widespread among journalists than the company originally claimed when it suggested only one rogue reporter, former royal editor Clive Goodman, was involved.

A News International spokesperson declined to give details of the Linklaters probe, other than to say it "started a number of weeks ago" and was "under the ultimate control" of the parent company News Corp.