Voice Profiles are now live in the UK. You need to go to Settings > Alexa Account > Recognised Voices in the Alexa app (you can't do this in the mobile app from what I can tell) and you will prompted to consent to the creation of a profile and then start the learning process on one of your devices.
It advises you to mute nearby devices, which is a good idea since some of the phrases used for learning your voice are like "Alexa, order item" or "Echo, call person" (it alternates between the different wake words in the phrases) and you wouldn't want a failure in ESP to result in another device acting on them.