June 30 (UPI) -- Britain is challenging Apple and Google for not allowing developers to pull users away from their app stores. The Competition and Markets Authority said Tuesday that Google and Apple have an "effective duopoly" on mobile phones by not allowing developers to engage with users or make purchases outside of the app stores. The CMA said at least 90% of mobile devices in the United Kingdom are running on Apple or Google platforms. It said allowing "steering" away from the platforms