Paranoia over leaks rather than hacking at the News of the World prompted Andy Coulson to send an e-mail ordering: "Do his phone", jurors at the trial were told yesterday.
The former editor denied the instruction had anything to do with hacking the phone of Calum Best, son of footballer George Best.
Coulson said an atmosphere of suspicion around a member of News of the World staff led to the decision to inspect his phone billing data.
He told the Old Bailey trial: "I was quite resistant to the idea of anybody working for me leaking stories but there was a growing body of evidence that was being put forward by some other people on the paper and in the end – reluctantly – I approved the request for billing data in relation to (the staff member)."
He told jurors he was "in no doubt" that the e-mail shown to the hacking trial was not an "instruction to anybody to hack anybody's phone".
The risk of stories being used by other papers was greater on a Sunday paper than on a daily and that let to "paranoia" over leaks, he said, adding: "It was very destructive. It was all too much time and too much effort."
In the event, there was no evidence to support the suspicions surrounding the reporter in question.
The trial was adjourned until 10am on Tuesday.