Ofcom has escalated its investigation into whether BSkyB remains a "fit and proper" owner of a broadcasting licence.

The media regulator has asked Rupert Murdoch's company, News Group Newspapers, publisher of the Sun and the now-defunct News of the World (NoW), to provide it with a series of documents relating to the civil litigation in which the media company is involved.

Ofcom has been gathering evidence since last summer, when it said it would consider whether phone-hacking allegations at the NoW were relevant to whether News Corp would be a fit and proper owner of the satellite broadcaster BSkyB.

The regulator has been monitoring publicly available evidence, but it has now called for documents that are not in the public domain.

A spokesman said: "Ofcom is gathering evidence which may assist it in assessing whether BSkyB is and remains fit and proper to continue to hold its broadcast licences.

"As part of this ongoing assessment, Ofcom has contacted News Group Newspapers requesting documents which it understands are held by the company and which may be relevant to this assessment. BSkyB is party to this correspondence.

"The documents Ofcom is seeking relate to the civil litigation cases. Ofcom is seeking to obtain documents that were ordered to be disclosed in the civil litigation between numerous complainants and News Group Newspapers."

Earlier on Thursday, Rupert Murdoch, the chairman and chief executive of News Corp, which owns a 39% stake in BSkyB, faced three hours of questioning at the Leveson inquiry into press standards.

His appearance followed revelations at the inquiry on Tuesday that the special adviser for Jeremy Hunt, the culture secretary, had allegedly passed sensitive information to a senior News Corp lobbyist regarding the company's £8bn takeover bid for BSkyB.

Last year, News Corp bowed to pressure and withdrew its takeover plans after the company admitted that the public uproar over phone hacking had made the climate too difficult. Earlier this month, Murdoch's son James resigned as BSkyB chairman.

As part of Ofcom's investigation, it will be considering all shareholders and directors of the company.