Another high-profile German politician has been stripped of a doctorate for plagiarism. This time the culprit tried to explain away his bad habit, blaming it on a stint at Oxford in the 1990s.

On Wednesday, the faculty of philosophy at the University of Bonn announced that it was annulling the doctorate awarded to MEP Jorgo Chatzimarkakis, a member of the liberal Free Democrats (FDP).

The scandal is the latest political plagiarism case exposed in recent months, following those of former defence minister Karl-Theodor zu Guttenberg and MEP Silvana Koch-Mehrin.

On Wednesday Bonn University said that Chatzimarkakis had used verbatim passages from other authors' work without using quotation marks. While he did mark the passages with footnotes, there was insufficient acknowledgment of the original authors.

Yet, the politician has insisted he thought his method was sound, saying he had picked it up at one of the most prestigious universities in the world while he was a research fellow at St Antony's College, Oxford University in 1995.

Speaking on Germany's premier political talkshow, Anne Will, in early July, he said that in Oxford, "they phrase things somewhat differently. They intertexualise, that is they make texts readable."

Bonn's dean of philosophy, Günther Schulz, said the method the politician had used was simply not acceptable: "He didn't use quotations marks, so the reader thinks that he is reading a text by Chatzimarkakis, when actually more than half the text is from other authors."

The FDP politician's comments so infuriated a couple of Germans studying at Oxford that they decided to take action.

Markus Gerstel, studying for a doctorate in systems biology, fired off a string of letters to various bodies within the universities, including St Antony's, alerting them to the slur on their reputations.

"It was really his mistake. I can't imagine that he learned that way of doing things in Oxford," he said, adding he thought it was in the university's interest to know what was being said about it in Germany.

Meanwhile, Jan Rosenow, doing a doctorate in energy policy, decided to write to Philipp Rösler, the leader of the FDP, to complain. "I got really annoyed. I think actually in the UK there is much more emphasis on plagiarism compared to Germany. And I felt that he was throwing dirt at my university."

Ruth Collier, head of the press office at Oxford University, said that the academic standards expected of Oxford students were the highest internationally accepted. "It's hard to believe there would have been encouragement to use substandard academic practices from Oxford."

Schulz said Bonn University had never accepted the excuse that this was common practice at Oxford, adding: "It is important that there are no bad feelings between German and British universities."

• This article was amended on 15 July 2011. In the original, a TV talk programme was misspelled as Anna Will, and a graduate student was misnamed as Markus Gestler. This has been corrected.