LONDON—  De La Rue, which has printed banknotes for the Bank of England since 1860, and also prints currency for 140 other countries, has issued a warning that there was “significant doubt” about its future. It is the largest banknote printer in the world, produces passports for 40 countries, and has designed 36 percent of all banknote denominations in circulation, De La Rue has suffered two major setbacks in the past year that have thrown the company’s future into question. In 2018, De La Rue lost the contract to print the United Kingdom’s new blue passports after Brexit is completed. That contract will go to a German printer . De La Rue also wrote off £18 million last year after Venezuela's central bank failed to pay .