News of the World publisher News International is facing a police investigation likely to assess tens of thousands of emails, phone calls and documents, as news breaks that chief executive Rebekah Brooks has stepped down following heightened accusations of phone hacking.

Police are understood to be trawling through thousands of emails containing potentially damning information, as investigators probe the alleged grave malpractice by News of the World journalists who were attempting to get a story. The FBI is understood to be beginning a similar investigation in the US.

News International’s  email trawl for its own ‘internal’ investigation four years ago only considered 2,500 messages – a small number when many journalists and executives each deal with hundreds of emails per day. News International is reported to have only handed over 300 of these emails to a law firm that was directing that investigation.

News International has also been accused of attempting to delete crucial emails, including reportedly demanding outsourcer HCL help it with this. HCL denies any involvement in such practices.

The news raised serious corporate governance questions, leaving businesses around the world looking for answers on their own email and document deletion issues.

A panel of experienced lawyers told Computerworld UK this week that deleting most emails was entirely legal for businesses. But when a business is facing investigations by law authorities or in civil suits, email deletion would be viewed as a potentially serious matter.

Danvers Baillieu, a senior associate at law firm Pinsent Masons, said: "If a company senses the faintest whiff of something like that, then they have to keep the documents. Otherwise the deletion of such emails could weigh against them in the eyes of a judge or jury."

The News of the World newspaper shut on Sunday, after a 158 year run. Since then, executives NI parent News Corp, including Rupert Murdoch and his son James, have been ordered to appear before the Commons Media, Sport and Culture Commons committee on Tuesday afternoon.