The search engine has form for this sort of thing. Two years it fired two boffins who criticised the biases built into its artificial intelligence systems.

Researcher, Satrajit Chatterjee, led a team of scientists in challenging a celebrated research paper, which appeared last year in the scientific journal Nature and said computers were able to design certain parts of a computer chip faster and better than human beings.

Chatterjee, 43, was fired in March, shortly after Google told his team that it would not publish a paper that rebutted some of the claims made in Nature, said four people familiar with the situation who were not permitted to speak openly on the matter.

Google confirmed in a written statement that Chatterjee had been "terminated with cause." Google declined to elaborate about Chatterjee's dismissal, but it offered a defence of the research he criticised and of its unwillingness to publish his assessment.