Earlier this month Amazon launched a feature in the US called Alexa Announcements, which let Echo users send one-way intercom-style messages from one Echo device to another. Now it's announced that feature willing be rolling out that feature to UK customers from today.
The idea behind Announcements is to send quick messages to other people in your house, without having to resort to shouting or text messages. Instead you simply say to your Echo "Alexa, announce that X" and the virtual assistant will relay that messages to other Echo's on your network. You can do the same thing with the command "Alexa, tell everyone Y".
Echo devices have had a proper intercom system for a while, letting Echo users single out specific devices on the network to launch two-way conversation. Announcements is similar, but it's designed for times when you want everyone to hear what you have to say without the possibility of them talking back. Obviously that would require you to have more than two Echo's in the house to make any noticeable difference, but seeing as how smart speaker ownership is starting to speed up (and the number of discounts some of them enjoy) that might not be such a ridiculous scenario.