Download the latest version of Signal app to your mobile device. You can download from the signal in App Store or Play store depending on IOS, Android Operating systems. If you can look through the signal.org website also you can easily download the latest version of the signal app to your mobile phone and also to signal desktop to your computer.
Signal app for the UK is also the same as other countries and also can download for your windows 10 computer PC. This is the same signal messaging app for windows.