Detectives said on Thursday they had arrested another reporter over allegations of phone hacking by journalists at the News of the World.

The arrest is the third in just over a week in a scandal that has already forced an admission of liability from owner News International and led to the resignation of Prime Minister David Cameron's spokesman.

Detectives are investigating claims that journalists on the weekly tabloid were hacking into the voicemails of members of the royal family, politicians, celebrities and sports stars.

Police said a 55-year-old man had been held on suspicion of conspiracy to unlawfully intercept communications and unlawful interception of mobile phones.

A source close to News International confirmed the man was one of the paper's senior reporters, James Weatherup.

Last week, detectives arrested Neville Thurlbeck, the paper's chief reporter, and Ian Edmondson, a former senior editor who was sacked after an internal inquiry.

There was no immediate comment from News International about the latest arrest.

Until last week, News International had always blamed rogue reporters for any hacking, first uncovered in 2005/6 when its royal reporter and a private detective were jailed for snooping on voicemail messages of royal aides.

But on Friday it admitted liability and said it would pay compensation in eight cases.

It has also written to nine others who claim their phones were hacked and who have started legal action against the group, asking them to provide more evidence.

Lawyers say the company could face a flood of claims which could cost 40 million pounds.

The Financial Times reported on Thursday that the agent who represents England footballer Wayne Rooney was also planning to sue the newspaper over claims his phone was hacked.

The scandal has embroiled the prime minister whose judgement has been called into question over his decision to appoint Andy Coulson as his media chief.

Coulson, who was the paper's editor when the hacking scandal broke, later resigned his Downing Street post although he always denied any knowledge of the practice.

The Guardian said on its website that Weatherup had been news editor at the paper under Coulson and was one of his inner circle of executives.