(Adds poll, background)
BERLIN Feb 26 German prosecutors have opened an investigation into a former minister in Chancellor Angela Merkel's cabinet on suspicion of betraying confidential information, a spokesman said on Wednesday, nearly two weeks after he resigned.
Former agriculture minister Hans-Peter Friedrich, a member of Merkel's Bavarian sister party, quit over accusations he leaked confidential information about a fellow lawmaker suspected of possessing child pornography.
"We have started proceedings", said a spokesman for Berlin prosecutors.
Friedrich had in October 2013 told the chairman of the Social Democrats (SPD), with whom the conservatives were in coalition talks, that the name SPD lawmaker Sebastian Edathy had come up in an international investigation into pornography.
The scandal rocked Merkel's new "grand coalition" only months after it was formed.
A Forsa poll showed on Wednesday that the SPD had suffered most from the scandal, which infuriated conservatives because it was an SPD lawmaker who revealed Friedrich's leak.
So far no senior SPD figures have quit but in the survey, the SPD were down 2 percentage points at 22 percent - its lowest level since the September election. Despite Friedrich's resignation, the conservative camp gained one percentage point to 41 percent.
Edathy, who quit parliament earlier this month citing poor health, has denied possessing child pornography.
The prosecutors said Friedrich did not enjoy immunity because the president of the Bundestag lower house had raised no objections in the 48 hours after they wrote to inform him of their intentions. (Reporting by Andreas Rinke; Writing by Madeline Chambers)