I'm a UK iPhone user. Google Maps turn-by-turn navigation has always used a US English voice for me, even though both Siri and Apple Maps use a British English voice. I was surprised recently to hear British English directions in Google Maps on another user's phone. I've never been able to find a setting to change it, beyond checking my Siri settings, so assumed I was stuck with a US voice.
How do I configure Google Maps to use a British English accent and British variant words?