Daniel Bahr also expressed anger after on Wednesday's Sueddeutsche Zeitung newspaper alleged that an employee of a company contracted by the German health ministry had handed the information to the lobbyist.

Speaking to reporters, Bahr urged "a speedy clarification of the case by the investigating authorities".

"I am hopping mad about so much criminal intent," he said.

The employee, who worked for a company responsible for computer technology at the health ministry, allegedly passed emails, draft legislation and other information to the freelance lobbyist, the newspaper reported.

It said that according to Berlin's public prosecutor, the lobbyist was working for the interests of pharmacists.

The apparent aim was to help the pharmacists' industry counter legislation under preparation, it said.

The alleged leaks were thought to have begun in 2010 and continued for around two years.

Bahr said that a legal case had been lodged in September and that searches were carried out in November at the ministry as well as at the premises of the employee and another person.

He also said that none of his emails or those of his predecessor Philipp Roesler were affected by the alleged incident and that it had not influenced him in his decision-making as minister.

The Federal Federation of German Pharmacy Associations expressed "great consternation" over the suspicion and said it was never its policy to "represent the interests of German pharmacists with a cheque book".

A health ministry spokesman told a regular government news conference that an investigation had been under way for about four weeks.