Drug companies are bracing themselves for the launch of a series of antitrust investigations in Europe after the European Commission published a highly critical report on industry practices.

The 426 page preliminary report by the commission’s Competition Directorate, which is to be followed by a final version next spring, highlights widespread legal tactics by drug companies to defend their patents. The commission says that such tactics have delayed the entry of cheaper generic drugs, at a cost of €3bn (£2.5bn; $3.8bn) since the start of the decade.

It cites instances of companies starting litigation to hold up competing products, filing multiple patent …