Apple Inc. and Alphabet Inc. risk a formal UK investigation over their dominance of web browsers on mobile phones, according to a provisional decision targeting the tech giants’ stranglehold on mobile operating systems.

Apple could be holding back innovation in smartphone browsers, according to a British regulatory report, which recommended that Apple's and Google's duopoly in mobile ecosystems should be investigated with its new powers.

Apple and Google aren't giving consumers a genuine choice of mobile web browsers, a British watchdog said Friday in a report that recommends they face an investigation under new U.K. digital rules taking effect next year.