The results of rigged animal tests that have plunged the German car industry into renewed turmoil were suppressed because they showed the opposite of what car-makers wanted, it has emerged.

Monkeys were forced to breathe diesel exhaust fumes from a VW Beetle for several hours in an attempt to prove they were not toxic in a study funded by Volkswagen, BMW and Daimler, the company that makes Mercedes.

But it has now emerged that the experiment found the exhaust was more harmful than fumes from a 20-year-old diesel car — despite the fact that the Beetle was fitted with software designed to lower emissions during tests.

The car-makers allegedly refused to pay for the tests, which were conducted in the US, after the results weren’t what they were expecting.

The details emerged as senior managers were suspended at BMW and Daimler in the wake of the scandal, in a sign the scandal is spreading beyond VW, the only company to admit responsibility so far.