Go to Settings, select Time & Language and click Region & Language. Make sure United Kingdom is selected in the dropdown, and remove English (United States) from the list of languages. Restart the machine.
Windows key plus space bar cycles through all installed languages. To prevent it happening, ensure that UK is set as the default, then remove the US keyboard.
Settings / Time & Language / Region & Language
Click on any installed language that you are not using, and choose "remove"
It happens after an upgrade Whistonian, but only if you have not removed the option. I am sure you have now removed the US default. It will not happen to w7 users, who are not of course subject to the new operating and security upgrades available on the latest and far superior operating system.