A private detective jailed for illegally intercepting voicemail messages on behalf of a journalist at one of Rupert Murdoch's British newspapers has been ordered to reveal who asked him to carry out the phone-hacking.

The demand by London's High Court will shed further light on how widespread the hacking practice was at the News of the World tabloid and add to the pressure on News International, the British newspaper arm of Murdoch's News Corp .

Glenn Mulcaire was jailed in 2007 along with the paper's ex-royal correspondent Clive Goodman for illegally accessing the voicemails of royal aides and five other figures including the model Elle Macpherson.

Lawyers for actor Steve Coogan, who believes he is a victim of phone-hacking and is suing News International, said on Friday the court had refused Mulcaire leave to appeal against a decision ordering him to reveal who instructed him to hack the phones.

John Kelly of law firm Schillings told Reuters that Mulcaire, who is suing News International himself after they stopped paying his legal fees, would have to answer their questions in a formal document to be filed at the court before September. This should be available for the public to see.

He will now have to identify exactly who at the News of the World asked him to access the mobile phones of the named individuals and who he provided the information to at the News of the World, Kelly said.

Mr Mulcaire is due to provide these answers by the end of the month and we await his answers with interest.

After Mulcaire and Goodman's conviction in 2007, News International repeatedly insisted that phone-hacking was limited to a single rogue reporter.

But in the face of civil action from Coogan and other figures, the company admitted earlier this year it had evidence that the practice was more widespread, prompting a new police inquiry.

Some executives, including Murdoch's son James, chairman of News International, are facing accusations that they knew about the illegal activities at a far earlier date than they had previously admitted.

Other senior figures, including former editorial staff on the now defunct paper, have been arrested by police probing allegations journalists on the News of the World illegally intercepted the voicemails of mobile phones of celebrities, politicians, as well as victims of crime and their families.

It has also caused embarrassment for Prime Minister David Cameron whose former media chief -- previously a News of the World editor -- is one of those to have been arrested as part of the probe.

PHONE-HACKING DETECTIVE ARRESTED

In a twist on Friday, London police said one of the detectives involved in the inquiry, named Operation Weeting, had been arrested on suspicion of leaking details about the case.

The Metropolitan Police's anti-corruption unit detained the 51-year-old detective constable at work on Thursday. He is accused of misconduct in a public office and has been released on police bail and suspended from duty.

I made it very clear when I took on this investigation the need for operational and information security, said Deputy Assistant Commissioner Sue Akers who is leading the inquiry.

It is hugely disappointing that this may not have been adhered to.

On Thursday, detectives arrested a senior Hollywood reporter from the News of the World, an arrest which was reported in detail by Britain's Guardian newspaper before any official announcement from the police.

Meanwhile, detectives from the Weeting team made their 14th arrest on Friday, a 35-year-old man who was held on suspicion of conspiring to unlawfully intercept voicemails. A source with knowledge of the inquiry named him as Dan Evans, a former feature writer on the tabloid.

He was detained after arriving by appointment at a London police station and later released on police bail until October.

(Additional reporting by Georgina Prodhan, editing by Rosalind Russell)

Hacking