German carmakers were engulfed in a new scandal on Monday after it emerged they had tested potentially dangerous exhaust fumes on human subjects.

A research group set up by Volkswagen, BMW and Daimler, the maker of Mercedes, deliberately exposed human test subjects to toxic exhaust chemicals for hours at a time in an attempt to prove they were not carcinogenic between 2012 and 2015.

Details of the human testing were exposed only days after it emerged that the carmakers had carried out similar tests on monkeys.

The revelations sent shockwaves through the German establishment. Barbara Hendricks, the German environment minister, described the experiments as “abominable”.

“These tests on monkey and humans cannot be justified ethically in any way,” a spokesman for Angela Merkel said. “The outrage felt by many people is completely understandable.”