The growing antitrust scrutiny of Google’s landmark settlement with book publishers has greatly added to the pressure on the internet company to back down on the most controversial parts of the deal before a key US court hearing in September, according to antitrust experts.

At the same time David Drummond, the company’s leading lawyer, said that Google would be open to changing the terms of the deal if a “compelling argument” was made by regulators, although he added: “We haven’t heard it.”