You can set up a Household Profile on your Alexa Devices. With Household Profiles, you can add another adult to your Amazon Household to listen to either users' content (for example, music and audiobooks) and manage shared features (for example, lists).
Joining a Household also gives you the option to share certain content purchases with other Household members across other Amazon devices and media apps.
Add a User to Your Household
Make sure the person you invite to your household is present.
From the left navigation panel in the Alexa app, select Settings.
Under Account, select Household Profile.
Follow the instructions for the second person to join your Amazon Household. During the process, pass your phone, tablet or laptop to the second person to enter their account information.
I don't have a 'Household' option in my settings. Are you sure this feature is available in the U.K.?
There is no multi user support for Alexa devices in the UK, households are as Rachel F says but in the UK Alexa devices are unable to distinguish between people, anyone can trigger it by saying Alexa and it will respond and work with the registered account. Mine has even played music in response to a TV advert.
What app are you using as I don't use apps but can see the household setting on this Alexa link, go into settings and scroll down to accounts where it is near the bottom.
I have just put the Android app on my phone and the household profile is in settings, if you click it BUT it just uses the browser to go to the main Amazon site.
I wonder if people who can't find it are using apps on iPhones etc, as households require card details and Apple take a % of transactions which Amazon will not pay I wonder if it is not available in iPhone apps, this would be similar to the Kindle app where iphone users can't use it to buy books but Android users can.