From the Guardian:
The information was passed in a letter to [actor and comedian] Steve Coogan‘s lawyers in accordance with a court order.
Mulcaire had applied for permission to appeal against the order, which was made in February, but this was denied and he was compelled to pass over the details by Friday.
His solicitor, Sarah Webb, from Payne Hicks Beach, said she could not reveal who the NoW employees were because of “confidentiality issues”.
Mulcaire was ordered to reveal who instructed him to access Coogan’s voicemails, as well as those of celebrities including Max Clifford and Elle Macpherson.
He was jailed for six months in 2007 for intercepting messages left on royal aides’ phones.
A spokeswoman for News International said the firm had no comment.
Here’s some background info about Mulcaire from Brian Cathcart at THE DAILY BEAST (August 22, 2011):
The man at the very center of the British phone-hacking scandal has proved remarkably adept at keeping his secrets. When the private investigator Glenn Mulcaire was first arrested in 2006 for hacking on behalf of News of the World he said nothing to police interrogators. Because he then pleaded guilty and no trial was necessary, he never faced cross-examination in court about what he had done.
Ever since his release in 2007, he has waged a sustained legal campaign to block the release of information about his activities to those hacking victims who have sued Rupert Murdoch’s U.K. company, News International. On the occasions when judges found against him, he has been quick to appeal to higher courts, further stretching and delaying the process.
For most of this time the documentation seized from his office and home in 2006 lay unexamined and unprocessed in trash bags in a police evidence pound.
Mulcaire, meanwhile, has made only one brief public statement, last month, in which he apologized to those he has hurt and pleaded that he acted under ‘relentless pressure’ from News of the World.
It is quite an achievement for the former professional soccer player now known to have been the hub of the newspaper’s hacking activity, a man who built up a directory of thousands of phone numbers and mobile PINS, and who, though never formally on the staff, was paid a salary of £102,000 plus extras.
Now, however, Mulcaire is being pushed into the spotlight and—as with almost every other recent development in this scandal—this looks like bad news for the Murdochs.
Part of Mulcaire’s problem is money. A month ago, James Murdoch, under questioning from members of Parliament, confirmed that his company had been paying for Mulcaire’s lawyers and, duly embarrassed, promised to halt that flow of cash.
In what British tabloids might call a “bizarre twist,” Mulcaire, a convicted criminal, is now suing his former employers in an apparent effort to force them to resume paying his legal bills.
What looks like a rift may, however, be something different, because it remains the case that Mulcaire’s legal interests and those of News International overlap considerably. Mulcaire’s reticence, after all, has always suited News International, whose principal tactic in the civil courts has been to avoid disclosure.
Who will he name as his controllers at News of the World? There are unlikely to be big surprises at this stage, since the police have been working out the answers over recent months and arresting people (all of whom, so far as we know, have denied wrongdoing). But this must be a landmark in this scandal, because, first, Mulcaire’s evidence is of such special importance, and second, it appears to be the beginning of the end of his resistance.
Once he starts making revelations, even under legal duress, his position is significantly altered. Having tried a policy of silence and failed, he may be better off adopting a policy of complete openness, and he is the person who knows most in this entire affair.