An investigation into a suspected breach of the Official Secrets Act by two senior police officers was dropped today.
Scotland Yard said there was not enough evidence against former Hampshire Assistant Chief Constable Steve Watts and an unnamed inspector to continue the inquiry.
A Metropolitan Police spokesman said no further action would be taken following advice from prosecutors.
Mr Watts was questioned under caution by police at a south London police station on 9 September last year and retired from the force a week later.
The previous day the second officer, an inspector, was arrested and interviewed by officers from the Metropolitan Police's specialist operations unit.
The two officers are believed to have been questioned over the unauthorised disclosure of information held in counter terrorism policy documents.
Hampshire Police said it would now conduct an internal inquiry into whether the serving officer should be subject to disciplinary action.
The Metropolitan Police spokesman said: "We can confirm that following advice from the Crown Prosecution Service on February 20 that there is insufficient evidence to provide realistic prospects of conviction no further action will be taken against an off-duty police officer who was arrested by the Metropolitan Police Service on September 8 2008."
Speaking about Mr Watts, he added "no further action will be taken against an off-duty police officer who was interviewed under caution".
A Hampshire Police spokesman said: "The constabulary will now consider whether or not misconduct proceedings are necessary in relation to the officer who still is serving in the force. The other officer has retired."
Hampshire Chief Constable Alex Marshall said: "Steve Watts retired from Hampshire Constabulary in September last year.
"It should be recognised that he served the force and the people of Hampshire and the Isle of Wight loyally for 32 years."