Given the sensitivities around Scappaticci, it is not clear why Scotland Yard failed to take any action against the News of the World or the private investigator when detectives seized the invoice in 2007. At the time, police chiefs were insisting criminality at the newspaper was confined to "one rogue reporter", Clive Goodman, who was jailed for phone-hacking in 2007.
The private investigator cannot be named for legal reasons, but, to clarify, he is not Glenn Mulcaire, convicted in 2007 in the original phone hacking trial. When the Independent approached the unnamed investigator, he claimed the private phone records were obtained via a police source. Despite his involvement in the attempted compromise of one of the British Army's most sensitive assets, the private investigator said he was confident he would not face any action.
The private investigator, who has a criminal record, said the phone records belonged to Scappaticci's wife, who was thought to have stayed in Northern Ireland while her husband was in the witness protection scheme in Britain.
The private detective said the News of the World was trying to track the army informant's whereabouts "on the mainland". He said they managed to "turn round" a possible number to a phone box in Liverpool which they believed could be used by Scappaticci.
Watch: Ex-UK editor Coulson convicted of phone hacking
Scotland Yard failed initially to take any action over the Scappaticci compromise.
However, the Met has taken a much greater interest in its implications since last August after a third party emailed it to Commander Neil Basu, who has overall charge of the myriad investigations into News International.
The source was summoned to New Scotland Yard, London, where he was debriefed by Basu, Detective Chief Superintendent Gordon Briggs and a senior Met lawyer. The invoice has also been emailed to Keith Vaz, chairman of the Home Affairs Committee.
Yesterday Vaz said: "It is clear we have not reached the end of the revelations relating to hacking.
Read more
* Rebekah Brooks on hacking verdict: 'I feel vindicated'
* David Cameron in trouble with phone hacking judge
"The Prime Minister promised that on the conclusion of the criminal investigation into phone hacking a full investigation into police involvement would be commenced. That time is drawing near ... I will be writing to the PM to ask what steps he is proposing and what his timetable is for the next inquiry which he rightly promised."
Last week, Coulson was convicted of conspiracy to hack mobile phones. Five other News of the World journalists pleaded guilty to similar offences.
After an eight-month trial, former News International chief executive Rebekah Brooks was acquitted of four charges.
- Independent