LONDON — Shortly after Scotland Yard began its initial criminal inquiry of phone hacking by The News of the World in 2006, five senior police investigators discovered that their own cellphone messages had been targeted by the tabloid and had most likely been listened to.

The disclosure, based on interviews with current and former officials, raises the question of whether senior investigators feared that if they aggressively investigated, The News of the World would punish them with splashy articles about their private lives. Some of their secrets, tabloid-ready, eventually emerged in other news outlets.

Those damaging allegations, about two of the senior officers’ private lives, involved charges that one had padded his expense reports and was involved in extramarital affairs and that the other used frequent flier miles accrued on the job for personal vacations.

“If it is true that police officers knew their phones had been hacked, it is a serious matter that requires immediate investigation,” said John Whittingdale, the chairman of the Culture, Media and Sport Select Committee, which investigated phone hacking. “It would be shocking.”